A sudden increase in energy or vivacity resulting from a moment of danger or intense activity. I've never had an adrenaline rush like I had from skydiving; I was buzzing with energy for hours afterward!

One who constantly seeks out the sudden increase of energy associated with dangerous activities, similar to the way drug addicts seek out the "high" achieved by drug use. I do about 10 skydives a year because I love the rush so much. People consider me a bit of an adrenaline junkie.