English Most likely, this refers to two-outcome surebets. For example, one of the most popular markets in football is Over 2,5 \ Under 2,5 (more or fewer than 2,5 goals will be scored in the match). There is no third option; either one bet or the other will win.
Accordingly, 3-bet surebets are 3-outcome surebets; for example, a football match may end with a win for the first team - a draw - a win for the second team, making 3 possible outcomes in total.
If you work with live surebets, it is safer to work with 2-bet surebets; with pre-match surebets, this is not important.
All surebet scanners allow their users to select the type of surebets that suits them in the settings, for example,
In the selected example, the user will be shown all surebets, both with two and with three outcomes