criterion, criteria

Criterion is a singular noun that means the “standard” or “rule” used to make a judgment or decision.

Criteria is the plural form of that word, although it is commonly misused as a singular word (what is your criteria?).

You may use data and agenda as singular words (they are plurals in Latin), but the rule on criteria remains: It’s a plural word.

Example: There are several criteria we use to judge the credentials of an applicant, but the most important criterion is writing ability.