xNL means the buyin size is x, where x is 100 big blinds. Occasionally there will be deep stacked games where the buyin is 200 big blinds. In this case a $200 buyin game with 50c, $1 blinds would still be a deepstacked 100NL game. There should be a link to a glossary in the beginners digest or whatever its called. Check the stickies.