Voice is the category of the verb which indicates relation of the predicate to the subject and the object. There are three voices in English: the active voice, the passive voice, and the neuter-reflexive voice.

The active voice shows that the person or thing denoted by the subject is the doer of the action expressed by the predicate.

The passive voice shows that the person or thing denoted by the subject is acted upon.

The neuter-reflexive voice shows that the action expressed by the predicate passes on to the subject. This voice is formed by means of a reflexive pronoun.

Helen lifted herself up and looked towards nurse. (Gaskell)
The truth was, Mary was dressing herself. (Gaskell)