An intransitive verb doesn't need, and can't take, a direct object to complete its meaning. While transitive verbs have an object, either direct or indirect, intransitive verbs may never have any kind of object.
Verbs of Motion
Intransitive verbs are generally verbs of being or motion (coming and going) that do not require an object to complete them. Intransitive verbs (mourir, dormir, neiger, planer) should not be confused with transitive verbs that take an indirect object (aller, parler). Meanwhile, certain transitive verbs (manger) can be used intransitively without an object (il mange), and certain intransitive verbs can be followed unconventionally by a direct object (Il pense l'univers).
Intransitive verbs, like transitive verbs, may be modified by adverbs or prepositional phrases (Il dort souvent au volant. He often sleeps at the wheel.)
There are several cases where a verb that may be transitive or intransitive in English must be translated by two different verbs in French: "to return" (retourner, rendre), "to leave" (partir, laisser, quitter).
The most common intransitive verbs are those that require être as the auxiliary verb in the passé composé and other compound tenses. They are verbs of motion such as aller, arriver, partir, sortir and tomber, that require no direct object. Some être verbs can be used transitively (with a direct object), and when this happens, these verbs need avoir instead of être as the helping verb. When this happens, there is a slight change in meaning. On the other hand, there are many intransitive verbs of motion that use avoir, such as marcher (to walk) and courir (to run).