What does the -f option mean for the git rm command? -

this question has answer here:

• when git rm -f used? 3 answers

i learning git through this online book. don't understand info git rm command:

if modified file , added index already, must force removal -f option. safety feature prevent accidental removal of data hasn’t yet been recorded in a snapshot , can’t recovered git.

english not native language. have problems correctly translating of quote... "recorded in snapshot" mean? "commited"?

i see git rm 123.txt the same git rm -f 123.txt, if 123.txt changed , added index (i.e. storage area, through add command): removes 123.txt index , working directory. so, don't understand -f option meaning. please, expand me.

additional tried read this:

the files being removed have identical tip of branch, , no updates contents can staged in index, though default behavior can overridden -f option.

also this:

-f
--force
override up-to-date check.

what "tip of branch"? -f option?

try make changes file in git repo , remove it. example:

 $ git status  # on branch master  # branch up-to-date 'origin/master'.  # nothing commit, working directory clean   $ echo "a" >> http.c 

and try remove it:

 $ git rm http.c 

you get:

git rm http.c error: following file has local modifications:     http.c 

so, -f/--force option allow remove it:

$ git rm -f http.c rm 'http.c'