I've had a harmless bump on the inside of my wrist forever. What could it be?

I met someone else who has this too, and we have no idea what it is. (I have one on my other wrist, but smaller.) It's about an inch and a quarter down from the top of the wrist. It's most noticeable when I tilt my hand back, stretching the skin. It's as if there is a soft, tiny pebble under the epidermis. Doesn't hurt or anything and there's no discoloration at all. I umed everyone had one up until recently. I've had it, I believe, my entire life. What causes these? I like mine. :-) It's like a secret on.