the activity of riding on a skateboard (= a narrow flat board with wheels underneath) that is longer and slightly wider than the usual type

Longboarding is essentially skateboarding on a wider and longer board. 长板运动本质上还是滑板运动，只是使用的滑板更宽、更长。

the activity of riding on waves on a traditional type of surfboard that is usually eight feet or more in length

It's a fantastic beach for longboarding. 这是一个非常适合长板冲浪的海滩。

Honolulu women's longboard surfing contest got under way yesterday. 檀香山女子长板冲浪比赛于昨日开赛。