Mtime

Time of last modification of a file (e.g. the data in the file has changed). The information is taken from the inode.

$ stat -s $file | tr ' ' '\n' | grep mtime
st_mtime=1130490970
$ date -r 1130490970
Fri Oct 28 11:16:10 CEST 2005
$ ls -lT $file
-rw-r--r--  1 root  wheel  33554432 Oct 28 11:16:10 2005 file

If a file has been modified the mtime will change to that date. The mtime can be changed in a file:

# date -r 0
Thu Jan  1 01:00:00 CET 1970
# touch -mt 197001010100.01 $file
# ls -lT $file                    
-rw-r--r--  1 root  wheel  33554432 Jan  1 01:00:01 1970 file

When a files mtime is changed the ctime will update naturally to the date when this happened.