An action/adventure/mystery/dramedy/all types of speculative fiction/crazy show (2004-2010) created by Jeffrey Lieber, J. J. Abrams and Damon Lindelof, and show-run by Lindelof and Carlton Cuse.
On September 22nd, 2004, Oceanic Flight 815, en route to Los Angeles from Sydney, breaks up in midair and crashes on a tropical island. Initially, forty-eight passengers somehow survive. Unfortunately, they soon come to learn that this is no ordinary island. On their first night, they hear the roars of a mysterious monster in the jungle (which the camera doesn't seem to want to get a shot of) that is capable of uprooting trees. Later, this monster mutilates the pilot, but not before the pilot reveals that the plane had lost contact with the ground, before steering over a thousand miles off course prior to the crash; which means that any rescuers would be looking in the wrong place, hence the odds of rescue are pretty much nil.
Stuck on the island, the survivors must learn to work together if they want to survive in this strange and hostile environment. This isn't easy, not only due to the dangers and resource scarcity on the island, but also because the most prominent characters are so utterly screwed up. All of them have something they're hiding in their pasts. There's a seemingly nice person who was actually a fugitive on the plane being extradited; a one-hit wonder ex-rockstar junkie ensnared in a battle with heroin addiction; and a former torturer desperately searching for the one they love. And that's just the beginning.
Their backstories are revealed in flashbacks, with each episode tending to focus on a specific character. In general, Anachronic Order is to be expected with this show particularly in the flashbacks, as are other Mind Screw style tricks; if there is a method of skewing the audience's perception of events by rearranging the order of the scenes, LOST has used it.
As the show goes on, the characters are forced to grow and change in response to their changed lives, and more and more questions arise as the secrets of the island, which seems to have supernatural properties, are slowly uncovered. Furthermore, flashbacks reveal more and more connections between the characters' pasts, beginning to suggest that it may be more than coincidence that this specific group of people was all on Flight 815 together with each other.
The show was famous at the time for its high production values (the pilot alone cost $14 million and led to the firing of a ABC executive for greenlighting such an expensive endeavor), inhumanly dense plotting, a tendency to raise more questions than it can answer, and somehow remaining a smash hit despite all these "hurdles". The show also heavily involved its fandom in the storytelling process through the parallel Alternate Reality Game The LOST Experience. The success of Lost inspired network TV to commission a slew of imitators (The Event, Jericho, Surface, Terra Nova, Invasion!, FlashForward (2009), Revolution, and J. J. Abrams's follow up show Alcatraz), all serious and densely plotted serialized dramas based around a central mystery and tinged with a sci-fi edge. Unfortunately most of these shows have failed to recapture the lightning and almost all of them were cancelled after one or two seasons. Honorable mention goes to Prison Break, while not a sci-fi show, it was the first out of the gate to capitalize on TV audience's newfound love for serialized dramas, it was also arguably the most critically-acclaimed and successful of the Lost-clones, running for four seasons.
Lostpedia (which the producers themselves occasionally namecheck in DVD commentaries for its expanse of knowledge) has exhaustively catalogued (almost) every aspect of Lost. If you want insight into the show or just want to learn some random statistics, it's definitely worth checking out.
Recaps and summation of the show here.
God loves you as He loved Jacob.