Definition of "jockeys"

Standing in the cavernous barracks clad only in my jockeys, shivering next to other miserable schlubs and being handled like a piece of beef with "mad cow" disease did nothing to improve my mood.

2004, Dan Peek, An American Band, page 131

"Are you for real? I’d think with those green eyes you'd be peeling the chicks off your jockeys before they peeled your jockeys off you!"

2010, Angelo J. Lagana III, Me Island, page 368