The process of tagging someones picture on the networking site Facebook.
"Hey Kass don't forget to facetag those pics from last night"
A Facetag is a Hashtag used on Facebook, but it does not do anything because Facebook is not Twitter.
"Facebook post: If 2 people (male and female) create 2 children. They have effectively replaced themselves (birthrate is "2.1") #BadatMATH"
"Comment on post: Hey baby.. Hashtags on Facebook don't do anything!"
"Response: Hashtags are used on Twitter by twits. That was a Facetag"