Here's another post that answers that exact question: https://bitcointalk.org/index.php?topic=2828892.0

Merit is gifted to you by other members on this forum. When you make a positive contribution through a post or thread other members may reward you with merit. Once you have two merits you will be given one sMerit, which you can spend on a post that you believe is valuable. Spending sMerits will not deplete your total balance of merits earned.