Cerie Xerox is a character on 30 Rock portrayed by Katrina Bowden.
Cerie is Liz's sexy assistant. Her last name was not mentioned in the first season, but in a "humorous" way from the show's runners, she would get one in the second season, thus the Xerox name.
She is also the youngest member on the show's staff but has yet to give out her age (Bowden was 18 when the series started).
Much of the humor associated with her character comes from the things she says to and assumes about Liz, though the show portrays this insensitivity as coming from her naïveté rather than genuine malice.