Any two rolls in sequence, one by each player, that leads to a position in the game where an opponent would no longer be willing to accept if he were offered a double. If your opponent would have accepted the cube prior to this sequence it is said that you have "lost your market" for not doubling beforehand. It is a matter of recognizing positions where your opponent has many bad rolls that could come up on his next toss of the dice.

a roll (more generally a roll by you and a roll by your opponent) after which he will drop a double (provided on this turn your opponent will take the double)

a two-roll sequence that raises your equity above your opponent's take point