Lay betting is an important part of sure betting.
The difference between a regular bet (also known as a back bet) and a lay bet, is that on a back bet you bet on a team/player to win. If you were to place a lay bet on the same team/player, you bet on that team/player NOT to win. You can place a lay bet on exchanges such as Betfair, Matchbook and Smarkets.
Read more about lay betting and see lay bet examples in the Ultimate guide to sure betting.