a phrase used to describe a word you can not think of because you don't know it. You use this phrase when you have no knowledge of the proper word to imply that you have simply forgotten. With use of this phrase, you appear no less intelligent, merely forgetful.
1. "Hey Marvin, whats the name of that actor... the one from Forrest Gump?"
"Aw damn, I totally know who you are talking about, the name is on the tip of my tongue..."
"Its okay, we all forget sometimes."
2. While playing charades:
"Oh no! I can tell what you are doing! it is on the tip of my tongue!!"
"TIMES UP! It was jitter-bug."
"See! I knew that, i just couldn't think of the word."