Most television writers are members of the Writers Guild Of America (WGA), the union that covers writers. The WGA was formed to deal with the AMPTP (Alliance of Motion Picture and Television Producers), which, contrary to its name, represents the interests of the major entertainment conglomerates rather than actual producers. The WGA has gone on several strikes to demand better conditions for professional writers, the most recent one occurring from 2007 to 2008.
When a writer strike is called, development on scripts ceases. This frequently leads to shortened seasons, late night hosts forced to improv entire shows, and wacky stunts, like the time Curtis Armstrong had to sing "Wooly Bully" when Moonlighting ran short. The most recent strike caused critically acclaimed dark comedy Pushing Daisies to shorten its season, and when it came back the next fall, it dropped in the ratings and got canceled, despite the cries from critics and fans for the show to be saved. And that was only that strike's most visible victim. It is also, in part, responsible for the increase in Reality Shows on television.
A writer's strike is like TV Strikes, but it affects film and is the more accurate term, given that when modern audiences refer to "a strike" they're usually referring to either the 1988 or 2007 WGA strike.