An adverb forming part of a phrasal or phrasal-prepositional verb - eg off, in
The plane took off slightly late.
He sent in the application .
I don't get on with John very well
When the adverb particle is used in a transitive phrasal verb, it is separable : it may occur after the noun phrase and must do so if a pronoun is used :
He sent in the application. or He sent the application in.
He sent it in. *He sent in it.