A '1x2' market is what is known as a win draw win market. You are placing a bet on a team win the match where there is also a possibility of a draw. This means the market has 3 outcomes, team 1 wins, draw, or team 2 wins.
If a match is a best of 1 or a best of 2, where a draw is possible, then the 1x2 market will be able to be bet on.
If you bet on one team to win, that team must win the match for the bet to win, if it is a draw or the other team wins, then the bet is a loss.
This is different to the "Push no draw" market where if it is a draw at the end of play, your bet will be refunded.