What does "shake off" mean?

Free oneself or get rid of something or someone, as in I've had a hard time shaking off this cold, or She forged ahead, shaking off all the other runners. It is also put as give someone the shake, as in We managed to give our pursuers the shake. The first term dates from the late 1300s; the slangy variant dates from the second half of the 1800s.