Backside
Also known as: BS
Direction of a trick or turn where the skater's back faces the obstacle or the outside of the curve.
Extended definition
It's the exact opposite of frontside and the other half of skating's directional vocabulary. In street, a backside grind or slide usually means entering with your back to the rail or ledge; in transition, turning with your back to the outside of the ramp. Backside tricks feel different and have their own mechanics: many skaters have one side way comfier than the other.
Origin / etymology
From surfing: the turn where the surfer has their back to the wave.