A criterion is the condition that SI.ENS-type functions use to select rows. It can be an exact value, a text, a comparison in quotation marks such as ">=100", or a concatenation with a cell. The wildcard characters ? and * stand for a single character and a sequence of characters, respectively.
Example
=NB.SI(A2:A100;">="&F1) // greater than or equal to the value of F1