Warp power was source of power used to operate a ship's warp engines, as the warp reactor was capable of producing what was described as "tremendous amounts of energy." (ENT: "Twilight") The amount of warp power applied to an engine's output determined the warp speed, i.e. velocity, at which a ship would travel.
Warp power was generated by a combination of having an optimum balance in the matter-antimatter mixture ratio, followed by the specified reaction sequence, that lead to the magnetic plasma be transferred to warp field generators. Warp power could be boosted by increasing the speed of the parallel subspace field processor to gain a quicker response time. (TNG: "Booby Trap")
Warp power was a consumable, its availability could be measured by percentage or converted to a time measurement. (TNG: "Lonely Among Us", "The Best of Both Worlds", "New Ground", "Emergence")
As well, it could be combined with impulse power to allow for a "massive thrust" in the direction traveled. (TOS: "The Immunity Syndrome")
Warp power could also be applied to other systems, including the shields/shield grid, tractor beam/tractor beam generator, sensor array, main deflector/main deflector dish, targeting scanners, phaser banks. (TOS: "Elaan of Troyius"; TNG: "Hero Worship", "The Nth Degree", "Deja Q", "The Masterpiece Society", "Schisms", "A Matter Of Time"; DS9: "Once More Unto the Breach"; VOY: "Warlord", "Prey", "Resistance", "Think Tank")