missing explanation of Stage 4 in GCC Development Plan document

[Honggyu Kim]

Hi all,

I would like to know about the stages of development plan so I checked the following article:
https://gcc.gnu.org/develop.html

I have reported a bug recently but didn't clearly understand the term "stage 4" here.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65358

Do you think "stage 4" explanation is missing in "GCC Development Plan" document?
If so, can anyone please explain it or write the description on the document?

Thanks,

Honggyu