What does balk mean?

Answer 1

When a pitcher stops while in motion or when a pitcher is set and makes any sudden movements or turning of the shoulder in order to confuse the batter. In this case, any runners on base advance 1 base.

Answer 2

In the sport of Baseball, a balk is a deceptive motion or feint, illegal within the sport, which is intended to deceive a runner.

It can also be used to refer to an uncultivated ridge formed in the open field system, caused by the action of ploughing.