Is there a rule about abstaining from eating meat on Fridays during Advent? I have looked at a number of sites and most of them say no.
Here are the prescribed times of abstinence from the Code of Canon Law (1983):
The days and times of penance for the universal Church are each Friday of the whole year and the season of Lent (canon 1250).
Abstinence from meat, or from some other food as determined by the episcopal conference, is to be observed on all Fridays, unless a solemnity should fall on a Friday. Abstinence and fasting are to be observed on Ash Wednesday and Good Friday (canon 1251).
The episcopal conference can determine more particular ways in which fasting and abstinence are to be observed. In place of abstinence or fasting it can substitute, in whole or in part, other forms of penance, especially works of charity and exercises of piety (canon 1253).
Advent is not mentioned at all by canon law as a time of abstinence. During Lent abstinence from meat, or from some other food determined by the particular national episcopal conference of an area in which a person resides, is required on the Fridays of Lent unless a solemnity falls on a Friday. For information on penitential disciplines legislated for Fridays outside of Lent, please see Since Tomorrow is Friday… by Jimmy Akin.