The time after which "adult" content can be shown. This is usually defined as programs with intense violence, coarse language, naughty bits, sexuality, lots of explosions, and characters who die with their eyes open.
The watershed varies from country to country. It's typically around 9:00 pm (as in the U.K., Canada, Ireland and Australia), but it can be as late as 10 pm (as in Germany or the United States) or it can be early as 8:30pm (as in New Zealand). Japan has laxer standards in general, but its concept of Otaku O'Clock starts as late as 11 pm or midnight. In many regions, though, the watershed is in the middle of Prime Time viewing; everything before the watershed is "family programming", whereas the shows afterwards are the more "adult" hit shows. This means that the fact that a show airs after the watershed doesn't mean that a lot of people won't be watching it.
The concept was largely popularized by the U.K., which uses the specific term to regulate TV content. (Interestingly, British radio doesn't have a watershed, just a list of prohibited bad words.) In the U.S., the related concept of Safe Harbor refers to a policy of the Federal Communications Commission; it's the time period in which the FCC won't go after you for airing "adult" programming (as long as it's not legally obscene).
As an aside, the term "watershed" comes from agriculture; it refers to an earthen barrier that prevents irrigation water from crossing into a neighboring field, allowing the two fields to run on different watering schedules (and thus house different crops). It's also applied on the larger scale of rivers with a watershed being an imaginary line separating the water that flows into one direction from that which flows into another as in the Continental Divide which separates rivers draining into the Atlantic from those draining into the Pacific. (The above definitions also gave rise to the phrase "watershed moment," which refers to any event that separates two historical periods. This has nothing to do with broadcasting.)
- Japan brings us Otaku O'Clock, a time period starting at around 11 pm and extending into the early morning in which the really risqué shows can be aired. These include anime series based on H-Games (albeit cleaned up for TV) and live-action dramas with more extreme content. Examples include a live action adaptation of the adult manga/anime Hen (known as Strange Love in the US), which had a scene of the two Schoolgirl Lesbians skinny dipping and making out in the school pool; and Invisible Girl Ea, revolving around a young woman who spends the entire series as an Invisible Streaker.
- North America has a few quirks with its watershed programming:
- The watershed time in the U.S. and Canada can get tricky because they span many time zones. If you get the East Coast feed in Hawaii, the watershed can start as early as 3:00 pm, and the really adult stuff can start at 6 or 7 pm. The West Coast feed is better by a few hours.
- The U.S. watershed doesn't seem to make much of a difference in content on network TV; writers are hesitant to use bad language on either side of the watershed. And the Moral Guardians are in full force, too; when NYPD Blue showed a glimpse of male backside, it caused quite an uproar despite this being post-watershed. The real distinction lies between the networks and cable; channels like HBO in particular are known to be much more relaxed in terms of content regulation.
- Canada's state-run broadcaster, the CBC, does not participate in the private networks' self-regulating Media Watchdog group. As such, they've been known to air some pretty bad language on the six o'clock news (you know, as long as it's relevant). That said, they're not out of the reach of the national Moral Guardians.
- Sometimes programming is long enough to span both the pre- and post-watershed periods, and only the bit before the watershed will be censored. For instance, CTV showed Erin Brockovich this way, and it got to air a triumphant "Fuck you!" right after the first post-watershed commercial break.
- The British watershed is not meant to be an absolute dividing line; in theory the watershed is at 9 pm, but in practice it's as late as 9:30 to give the more sensitive viewers time to clear out. Similarly, films rated 15 will start airing earlier than films rated 18. Tamer shows and films might start airing at 8:30 on the reasoning that most of the film would be after the watershed. ITV in particular liked to needle the Moral Guardians by starting their dramas at 8:30 and avoiding violence, swearing, and nudity for the first half-hour — after which all bets were off.
- In The Netherlands, the watershed starts at 10 pm; no content with a 16 rating may be aired before that time. But after the Dutch watershed, anything goes, even hardcore pornography. The porn classic Deep Throat was even aired on a publicly-funded network after the watershed.
- The Latin American watershed is typically 10 pm; after that, the networks like to start airing telenovelas that are considerably Hotter and Sexier (and often Darker and Edgier).
- The Australian watershed can vary, but the absolute limit is 10 pm. After that, networks can show movies and shows completely uncensored, even if they would otherwise get an MA or R rating. Advertising will also get Hotter and Sexier as it gets closer to midnight.
- Out of all of the countries that started the watershed at 9 or 10pm, New Zealand starts the watershed much early at 8:30pm. Having an AO rating, itís not quiet enough. Programs with much stronger content would start 1 hour later at 9:30pm with a special rating called AO 9:30pm. However this may not be easy as it looks, the BSA are very strict about promos that airs within the pre-watershed time. Adverts in NZ are classified too (which no other countries would do) depending on whatís appropriate for family viewing and whatís not or even not appropriate for NZ screens. https://bsa.govt.nz/images/03_BSA_FREE-TO-AIR-TV_CLASSIFICATIONS_DRAFT.pdf https://bsa.govt.nz/images/codebook/Free_to_Air_TV_Code.pdf
- The British police drama The Bill is an interesting case study. It started out in 1984 as a post-watershed series, meaning that it had liberal cases of sex, violence, and nudity. Then in 1988, the production team decided to move it before the watershed, meaning that everything was toned down and the show as a whole was Lighter and Softer. It ran in this slot for most of its life, before the executives decided to move it back to 9 pm in 2009.
- Doctor Who airs before the watershed, but pushes the envelope to see what it can get away with in that timeslot. It airs on Saturday evening in a primetime slot, and it's gotten away with an infamously high body count, graphic violence, male-on-male and female-on-female kissing, bondage scenes, Davros' shirtless scene, and characters dying with their eyes open.
- Some Top Gear specials would air after the watershed, and the presenters would be aware of it. For instance, in the "Top Gear Ground Force" special, an annoyed James May stopped to verify that the special would be aired post-watershed before dropping a Precision F-Strike. (Well, he tried before a hard cut to Richard Hammond.)
- The Late Late Show was known to hang a lampshade on the phenomenon, especially when Craig Ferguson does a lot of swearing, even though it would be censored anyway. The censors did, however, allow Robot Buddy Geoff Peterson to get away with a hand gesture resembling masturbation because he didn't have genitalia.
- One of the most notable breaches of the watershed in Britain was the infamous Bill Grundy interview with the Sex Pistols in 1976. Grundy provoked them into saying all sorts of swear words during prime time viewing hours.
- Everybody Loves Raymond ran into some weird watershed-related censorship on British TV. It aired on Channel Four, which wanted to re-air the episodes the next morning for people who missed them, and as such decided to use pre-watershed censorship standards on a post-watershed show. In particular, Channel Four refused to air two Season Six episodes, "Marie's Statue" (suggestive artwork) and "No Roll!" (Ray and Debra's sex life), in spite of the fact that these episodes air with no problems in the notoriously prudish U.S.
- Nick Jr.'s "Nick Mom" lineup, geared towards the moms of their usual audience, had a problem with their West Coast feeds. People there were seeing (for example) Stand-Up Comedy routines about sex, periods, vaginas, and all that fun stuff...at about 6:30 or 7 PM their time. (See the East Coast West Coast feed problem mentioned above.) This caused controversy, and the channel responded by dialing it back a notch...which caused an even greater decline in viewership. Ultimately, the "Nick Mom" block was discontinued.
- Sky's Cinema channels gets around the watershed restrictions by demanding viewers enter a (customisable) PIN code before viewing a movie with a 12 rating or up.
- Although the "watershed" cut-off has been stereotyped as suggesting every show airing thereafter is adults-only, there is no hard and fast rule saying this has to be the case. In the UK, for example, both the BBC and ITV have aired family-friendly programming past the 9 p.m. point. Examples include the 2014 Doctor Who episode "Mummy on the Orient Express" which was scheduled so that the second half of the episode aired past watershed (leading to some complaints), and the historical drama series Victoria which, despite being scheduled for 9 p.m. and touching on topics such as sex, manages to do so without going beyond a PG (or 12) rating.