Generally I think of a catchphrase as being a phrase that is regularly repeated by a character or person to the point that it becomes an immediately recognizable part of their identity. The definitions I've found are a bit more vague though. (Merriam-Webster)
A word or expression that is used repeatedly and conveniently to represent or characterize a person, group, idea, or point of view
I recently heard someone refer to Bogart's line in Casablanca "Here's looking at you kid" as a catchphrase. I wouldn't consider this a catchphrase, just from my own understanding of the word, but I'm curious if it actually is. That phrase is certainly an immediately recognizable part of Rick Blaine's (and Bogart's) identity, but not as a result of him regularly repeating it.
So is an iconic phrase such as "Here's looking at you kid" a catchphrase or is that a misuse of the word?