Well first, there isn't any National Commission on the Status of Park Tricks. But according to Snowboard Addiction anyway, backside means you approach the feature to your heelside (backside). Doesn't matter if you hop into a boardslide (nose over feature) or lipslide (tail over feature), it's backside. Approach from the toeside and it's frontside.
This raises the question of what you call them if you're using a ride-on feature and approaching centered.