When I was a teacher of English to immigrants, I often had to explain to puzzled students that word meanings can change. Language is in flux. Words that meant one thing when I was young, may now mean something quite different. (Words like "neat," "cool," and "wicked" come to mind.) New words and expressions - such as those pertaining to the internet, like "wifi" and "blog" - are constantly being created as well.
After a friend's cat climbed onto my shoulder, I was informed that Sesame (the cat in the picture) was a "shoulder cat".
Googling the term, I found a number of You Tube videos and online articles explaining what "shoulder cats" were - their personalities, etc.
But when I looked the expression up on the online Urban Dictionary, I couldn't find it. When it's too new to appear in the Urban Dictionary, it's really new!