In Dutch, there are many verbs that consist of a verb and another word.
This other word can be an adverb:
goed (well) | goedkeuren | to approve
hard (hard, fast, tough) | hardlopen | to jog, to run
zwart (black) | zwartrijden | to travel without a ticket
But most compound verbs consist of a verb and a preposition, e.g. _aan_ (on, to, at), _om_ (about, around, down, to), _achter_ (behind, beyond), _onder_ (under), etc.
When combined with a verb, these prepositions are technically no longer prepositions. But we will refer to them as prepositional prefixes anyway.
Separable and inseparable compound verbs
Among the compound verbs, we can distinguish between separable and inseparable compound verbs. The names speak for themselves: separable verbs can be split into a verb and a prefix (a preposition or adverb), inseparable verbs cannot.