What is the meaning of Gulp?

The usual amount swallowed.

The sound of swallowing, sometimes indicating fear.

An unspecified small number of bytes, often two.

To swallow eagerly, or in large draughts; to swallow up; to take down in one swallow.

To react nervously by swallowing.

An indication of (the sound of) an involuntary fear reaction in the form of a swallowing motion.

fly; opening in a man's pants to facilitate relieving himself

gulp (expresses fear)

lock

Source: wiktionary.org