Skateboarding
For performing rotational tricks on flat ground, frontside means that for the first 90-180 degrees of the rotation, the rider can see ahead in the direction of travel. For a rider traveling in the "regular" stance (left foot leading), this means they rotate the given degrees of the rotation traveling counter-clockwise (as facing the direction of travel). A rider doing a backside rotation/trick is rotating clockwise.
When riding fakie/switch, the term is reversed. For example, a rider in the "goofy" stance (right foot leading) does a frontside 180 when he/she rotates 180 degrees clockwise.
Read more about this topic: Frontside