double sente; move that is sente for either player
In go, a move that gives the initiative (sente) to whichever player plays it; both sides gain an advantage by taking it. Compare 両後手 (double gote).
This corner move is double sente, so whichever side plays it gains an advantage.
両先手の場所は早めに打たないと相手に取られる。
You should play a double-sente point early, or your opponent will take it.
先手 generally means having the initiative or a move that keeps sente; 両先手 is a specific case where the move is sente for both sides.
Compound of 両 (both) and 先手 (sente, initiative in go). The term is specific to go terminology.