What does "intransitive" mean?

Intransitive: (Gram.) Not transitive; not passing over tas, an intransitive verb, e. g., the bird flies; the dog runs. Note: Intransitive verbs have no passive form. Some verbs which appear at first sight to be intransitive are in reality, or were originally, transitive verbs with a reflexive or other object omitted; as, he keeps (i. e., himself) aloof from danger. Intransitive verbs may take a noun of kindred signification for a cognate object; as, he died the death of a hero; he dreamed a dream. Some intransitive verbs, by the addition of a preposition, become transitive, and so admit of a passive voice; as, the man laughed at; he was laughed at by the man.