The Middle Voice, as opposed to either the Active Voice or the Passive Voice, is a linguistic curiosity. In languages including Icelandic and Ancient Greek, there is a specific form for it, whereas in other languages such as English or Swedish, the sense conveyed by the middle voice is expressed using one of the other voices. Sentences which would (where possible) employ the middle voice are:

The cat and the rat fought for an hour.
The house burned down.

In English, these usages tend to become active, whilst in Swedish they are often expressed using the -s passive. Latin employs deponent and semi-deponent verbs to make up for its lack of a proper middle.