A game where the goal is to have uncontested possession of the flag when the clock runs out. If more than one team is contesting the flag when the game's time-limit has run out then the game will continue until either one team has had uncontested possession for 3 seconds, or all the other players have died - in the latter case the game ends as soon as only one player/team is surviving.
One winning strategy is to use an extremely defensive force and establish a strong position within attack distance of the flag, where everyone can see you. Fight off and initiate probing attacks on your enemies and, when the clock dwindles, descend on the flag. Although technically it's a strategy with a reasonable chance of success or at least survival to the end of the game - especially for less-skilled players, lingering in your initial starting position and then rushing the flag at the end after your opponents have weakened themselves battling each other is generally considered cheap/rude (some would say cowardly) and un-sportsman-like. This is known as "camping" and is widely derided though it is in reality one of the most effective ways to ensure you survive with enough units to make a strong end-game play. Partial camping (not racing to the flag but not hanging back until the very end) doesn't carry the same stigma at all.
[Part of the negative opinion of 'camping' is from individuals who don't really care all that much about different game types and who play every game as a variation of body-count/survival of the fittest. Since their goal is to defeat everyone and rack up the most kills, if you stay away from combat while they are busy fighting everyone else and at the end of the game you waltz into the flag with 100% of your team intact and and win because they were down to 30% strength because they lost 70% of their force wiping out the other players they will feel like you "cheated". You didn't, you played the game-type to win - but you should be aware of the potential dynamic.