What does T mean?

I have some questions about C language.

One of them is what t means. As we all know, there are lots of user-defined types such as time_t and size_t in C language.

It puzzled me for a long time. However, I am so lucky today. I found a word 'typedef' when I read “C: a reference manual”. I think I suddenly realized what t means.

May t be short for typedef, and it means a user-defined type