If you're driven, you're strongly compelled or motivated to achieve a goal. If you're a driven gymnast, you spend hours in the gym each night perfecting your balance beam routine.
If you know someone who is incredibly ambitious and hard working, you can call them driven. It takes a driven student to make it through medical school, and a driven dog musher to complete the Iditarod. In other words, you need drive, or determination, to achieve these things. Driven can also mean "moved and piled into drifts by wind," often in the phrase "driven snow." When combined with another noun, it can mean "propelled or powered," as in "a wind-driven boat."