Tip: See my list of the 
MostThe media seem to have been plagued with expressions like “the criteria is” lately. Unfortunately, such expressions are incorrect because “criteria” is a plural noun; using it as a singular noun is essentially the same as saying “a houses is”.
If “criteria” is the plural, what’s the singular? The word is based on the Greek pattern -on → -a, so the singular form is criterion. For example:
correct The main criterion is as follows.
correct The main criteria are as follows.
wrong The main criteria is as follows.
correct That’s a very important criterion.
correct Those are very important criteria.
wrong That’s a very important criteria.
correct This criterion was decided upon by the committee.
correct These criteria were decided upon by the committee.
wrong This criteria was decided upon by the committee.
correct There’s only one criterion.
wrong There’s only one criteria.
One could argue that since what is considered correct is decided by usage, saying “a criteria” should be acceptable (as it has become somewhat widespread). However, no major dictionary or manual of style endorses such usage, and most educated native speakers find it wrong, so there is no good reason to use “criteria” as a singular noun.
