What is the meaning of phrase on tip your tongue?

The phrase "on the tip of your tongue" means that you know something, but you can't quite remember it at that moment. It's like the answer is right there, ready to be said, but you just can't quite grasp it.

Example:

"I know I've seen that actor in another movie, but his name is just on the tip of my tongue."

The phrase is often used humorously when someone is struggling to remember a specific word or piece of information.