Sexual act. Is a metaphore for engaging in the act of vaginal/clitreral stimmulaton using the erect male member/penis, making the female wet, or indeed the female using the wet vagina to rub/massage/stimulate the unerect penis. The metaphre being the male meber the board, the female the wave. Where penatration/intercourse would be in the ocean, to surf is to ride upon the wetness. This sexual act can be used for forplay or afterplay. Have fun and ride the waves.
''We didn't go all the way, we just surfed.''
''Surfing a really great way to get off while your waiting for your parnter to be - ready.''