In Second Life, the day an avatar was "born" or created is called its "rez-day," since "rez" (derived from "resolution") is the word used when something is made to appear in SL. That date is listed in the avatar's profile.
My darling Patrice was rezzed a year ago today, on December 21, 2005. Her current profile does not reflect this because the avatar Patrice Cournoyer is kind of Patrice version 2.0. For various reasons, some people leave behind their first avatar and give themselves a fresh start.
So happy rez-day, Patrice! And a merry solstice to all—the shortest day for those of us in the north, and the longest day for those south of the equator.