Mining is the action of a worker unit to gather minerals. In the game, the Protoss has the best mining rate out of all the races due to the unit collision shape of the Nexus. On the other hand, Terran is the slowest miner out of all the races due to the smaller collision hitbox of the Command Center. Contrary to popular belief, all workers move and accelerate at the same speed -- it is only due to the shape of the resource gathering center that mining rate differs between races.
The relative mining efficiency of workers is scv mining at 100% efficiency, drone at 182/174 = 105% efficiency and probe at 182/154 = 118% efficiency, based on the mining animation lengths.