From the earlier question:
I would like to now what the 'tmp' part is. Is it 'temp/temporary'. As you can see from the earlier question, that part wasn't answered.
tmp may be short for temporary (as in transient) since these files are, like log files, periodically rotated/truncated. The
wtmp files also initially resided in
/tmp when they were introduced in Version 3 AT&T Unix.
tmp could nowadays be read as an abbreviation of timestamp.
tm is also a common abbreviation of time (see, e.g., the manual for the
ctime() C function and the
time.h header) and these files contain the timestamps for system events relating to users logging in.
utmp likely comes from user.
btmp (on systems that has it) likely comes from bad (bad logins).
wtmp may come from who (as in "who was logged in?"), but not from
w (the utilities) as they use
utmp and not