Meaning of 'f' in the os.F_OK mode in the os.access() method

Question

I am trying to understand what the individual letters stand for in the os.access() method modes. The others are clear (Capitalized letter for clarity):

os.R_OK - checks for Readability

os.W_OK - checks for Writability

os.X_OK - checks for eXecutability

but what does the F stand for in os.F_OK? Existence doesn't have an 'F' in it.

Answer 1

from man page:

F_OK tests for the existence of the file.

may be F_OK for File existence OK.