Era vulgaris, Latin for "common era" and frequently abbreviated as "e.v." or "EV," is used to denote Gregorian calendar years after Christ.
Like the English equivalent, "CE," it is used instead of the Christian "AD" (which stands for Anno Domini or "the year of our Lord") because Thelema does not identify the birth of Christ with the beginning of our Era.
Likewise in English, "BCE," or "Before the Common Era" is used in place of the Christian "BC," which is an abbreviation of "Before Christ." The Latin equivalent of "BCE" would probably be "AEV," which is an abbreviation of ante-era vulgaris, or "PEV," an abbreviation of pre-era vulgaris.
See Calendar for a full description of the Thelemic Calendar and its notation.