Decathlon was a sports event which consisted of ten different disciplines.
Irina Karlovassi won a silver medal in the Olympic decathlon in the late 20th century. (ENT: "Cold Station 12")
B'Elanna Torres was on the decathlon team during her two years at Starfleet Academy. (VOY: "Basics, Part II")
Today, the decathlon is primarily considered a man's competition, women competing in the heptathlon instead.
The script of Star Trek Generations had Scotty commenting that Kirk's extreme activities made it seem like he was "running a bloody decathlon across the galaxy". Kirk's "decathlon" included rapelling the crystalline trench, rafting down lava flows, and orbital skydiving.