'weren't' is the contracted form of 'were not.' It's the past tense negative form of the verb 'be' used with plural subjects, as well as with the singular second person (you) and singular and plural third person when referring to a state of being or existence.
'weren't' is used to form negative statements in the past tense. It is used with plural subjects (they, we) and with the singular second person (you). It can also be used with singular third person in some dialects or informal speech.
They weren't at the party last night.
You weren't listening to me, were you?
We weren't aware of the changes.
a common mistake is using 'wasn't' with plural subjects. For example, 'They wasn't there' is incorrect. It should be 'They weren't there.' In standard English, 'He/she/it weren't' is considered incorrect. The correct form is 'He/she/it wasn't.' However, 'weren't' is sometimes used in place of 'wasn't' in informal speech or certain dialects. 'Weren't' is also used in some hypothetical or wishful statements, like 'I wish I weren't here.'