Abbreviation of the Latin, verbum intransitum, (or verb intransitive) often seen in dictionaries.

An intransitive verb is an action verb that does not have a direct object. The action is still being done, but it is not being done to anything or anyone else.

Most verbs can be intransitive or transitive depending on the sentence. (a notable exception: to go is always intransitive.

Transitive: He flies a kite. (The verb flies has a direct object, kite.)
Intransitive: He flies in airplanes frequently. (The verb flies has no direct object.)