Criteria is typically a plural noun referring to standards on which a judgement can be made. Its singular form is criterion, but evidence shows that criteria is frequently used as a singular as well as a plural.

Criteria are often the particular requirements that someone or something must meet in order to be considered or qualify for something. An applicant for a job may be evaluated based on several …

plural of criterion (Definition of criteria from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)

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Criterion is defined as “a standard on which a judgment or decision may be based” or “a characterizing mark or trait.” The former of these is the meaning in question when one says, “An important criterion …

Just 16 percent said having knowledge and skills that apply to a specific field is the most important criteria they seek. An "ethnic" membership criterion that one would be embarrassed to invoke for any …

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In standard usage, the plural is generally criteria, although criterions is sometimes used as well. Properly speaking, the form criteria should never be a singular noun, and phrases like this criteria and single …

Definition of criterion noun in Oxford Advanced Learner's Dictionary. Meaning, pronunciation, picture, example sentences, grammar, usage notes, synonyms and more.

Although criteria is sometimes used as a singular, most often in speech and rather infrequently in edited prose, it continues strongly in use as a plural in standard English, with criterion as the singular.