Criterion means a standard used for determination. Criterion is singular and has two plural forms: criteria and criterions. Both plural forms are acceptable, which can create some confusion. Most words do not have more than one plural form, and no clear criterion (pun intended) exists for determining when to use each or either one. The choice is simply left to the writer.
Consider the example sentences in the cropped graphic at left. The writer uses criteria and one of its plural forms correctly. Criteria, used in the first sentence, is the plural form more frequently used by writers. But that first sentence would be just as grammatically correct if it appeared like this:
Whatever you choose, be consistent with your criterion for making its plural. (Yeah, I love puns. Could you tell?) More effective writing applies the criteria of good writing consistently. And more effective writing makes a better presentation of both you and the brands you represent.