Term: Particles

A particle is a word that does not fit into the conventional grammatical categories the word 'to' can act as a preposition describing direction; she's gone to Antwerp. When 'to' is used with a verb in the infinitive, 'to abide' 'to do' etc., it is a particle, satisfying a grammatical function, but without an easily defined meaning. The term is also often employed for the words that make up a phrasal verb. This is because words that are familiar as prepositions, which link words, are functioning in a different manner:

The plane took off an hour late. ('off' changes the meaning of the verb but is not linking words or expressing direction, location, time or possession, which it would if it were acting as a preposition. Hence many people prefer to call words like this particles in phrasal verbs.)