Friends with benefits is the relationship where you are involved in a sexual relationship with that person, but without being emotionally attached
FWB means a relationship where two people get intimate physically. Still, they are not bound together with any expectations, committed to one another, and not obligated to tell one another the reason if they suddenly decide not to pursue the other person anymore.
Many people are more into the casual hook-up side of the relationship rather than getting seriously and emotionally invested in it. This could be possible reasons behind the FWB.
Are you the emotional type? Then try to get yourself involved in friends with benefits relationship. The person you like might be only interested in friends-with-benefits. It is best to avoid the situation to save yourself from the chance of heartbreak.