Name day
From A Wiki of Ice and Fire
Nameday is the Westeros equivalent to a birthday. The day a child is born he/she is also given a name that day so a persons age is recorded with his/her nameday as the beginning. The only exception is for Wildling births, as wildlings do not name their children till their child reaches the age of two.
See also
Customs for additional information on customs and traditions of westeros.