It's when you do a hard cardio workout.
"Man we definitely did a hardio run today with that 10 mile run."
by athena4peace August 12, 2008
Intense sexual intercourse consisting of advanced positions, rapid thrusting, accelerated heart rate & a lot of sweat.
After lifting, my girl and I had a serious hardio sesh.
by Meatball1985 July 08, 2014