The name of a theory?

Question

This theory is that other people are all in your mind. Maybe, for example, whoever answers my question is a figment of my imagination...it's like I can only trust the fact that I am here because I know my own thoughts? Haha I'm not a believer in it but I think it's interesting, and wish I could remember the name of it.

Answer 1

now then, you say "Maybe, for example, whoever answers my question is a figment of my imagination", but, what if you are a figment of my imagination.