Verbs
transitiv / intransitiv
In English: transitive / intransitive
A transitive verb takes an accusative object (kaufen, lesen); an intransitive verb does not (schlafen, gehen). This matters twice in German: only transitive verbs form a full passive, and transitive verbs build their Perfekt with haben.
Example: Sie liest einen Roman. (transitive) Das Baby schläft. (intransitive)