Sente is a Japanese
word describing a very important concept in the game of Go
). It translates as something like "initiative
Basically, if it is your turn to play and your opponent's last move doesn't necessitate an immediate a response, you have sente. You can play anywhere on the board that you like, solidifying your territory, enlarging your moyo, attacking one of your opponent's weak groups, etc. In other words, you get to choose the direction the game will take next.
Obviously, having sente is very important, so learning how to keep it, and how to take it from your opponent are crucial elements of Go strategy.
A move is called sente if, after the sequence that it starts has been played out, the player who started it still has sente. A move is called gote if, the other player gains sente after the sequence is played out. Obviously, if a move is sente, and is beneficial to you, you should play it (unless it would render a more valuable move impossible or gote).
Sente is relative, however. If, at any point in a sequence of moves, you feel that taking sente is more valuable than responding locally, you can tenuki (play elsewhere) and thereby steal sente from your opponent, rendering his sequence gote in exchange for allowing him to gain some extra advantage locally.
See also double-sente and reverse-sente.