Copping a feel on a girl without ever making out. Most commonly occurs at parties or dance clubs. Named for the circumstance in baseball when a player hits a ball and it bounces over the wall. He automatically advances to second base.
Person 1: Dude, did you see me grabbing that girl's tit when we were dancing? I totally just got to second base in like 5 minutes.
Person 2: I'm not sure if that qualifies as second base. It's more like a ground rule double.