What is balking in baseball?

Answer 1

An illegal movement made by the pitcher before he pitches the ball. Here is a mini article I found from Wikipedia on a few actions.

Balk actions

A pitcher is restricted to a certain set of motions and one of two basic pitching positions before and during a pitch; if these regulations are violated with one or more runners on base, a balk is called.

With a runner on base and the pitcher on or astride (with one leg on each side of) the rubber, it is a balk[2] when the pitcher:

• switches his pitching position from the windup to the set (or vice versa) without properly disengaging the rubber;
• while on the rubber, makes a motion associated with his pitch and does not complete the delivery;
• when pitching from the set position, fails to make a complete stop with his hands together before beginning to pitch;
• throws from the mound to a base without stepping toward (gaining distance in the direction of) that base;
• throws or feints a throw from the rubber to an unoccupied base, unless a play is imminent;
• steps or feints from the rubber to first base without completing the throw (doing so to second or third base is legal);
• delivers a quick return, a pitch thrown right after receiving the ball back, with intent to catch the batter off-guard;
• drops the ball while on the rubber, even if by accident, if the ball does not subsequently cross a foul line;
• while intentionally walking a batter, releases a pitch while the catcher is out of his box with one or both feet (rarely enforced);
• unnecessarily delays the game (rarely enforced);
• pitches while facing away from the batter;
• after bringing his hands together on the rubber, separates them except in making a pitch or a throw;
• stands on or astride the rubber without the ball, or mimics a pitch without the ball; or
• throws to first when the first baseman, because of his distance from the base, is unable to make a play on the runner there.

The pitcher's acts of spitting on the ball, defacing or altering the ball, rubbing the ball on the clothing or body, or applying a foreign substance to the ball are not balks, however it will result in the pitcher's ejection from the game if caught.