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Wiktionary
irrealis mood

n. (context grammar English) A category of grammatical moods that indicate that a certain situation or action is not known to happen, or have happened, as the speaker is talking.

Wikipedia
Irrealis mood

Irrealis moods ( abbreviated ) are the main set of grammatical moods that indicate that a certain situation or action is not known to have happened as the speaker is talking. This contrasts with the realis moods.

Every language has a formula for the unreal. Some languages have as many as five levels of "unreality".