mtime is short for modification time or st_mtime, from the stat
In a unix filesystem, the mtime represents the last time a file was written to.
The mtime is updated with the current time if any system calls are used on the
file that create it or modify the data in the file. Also, the utime system call
may set mtime.
The ls command by default uses mtime for the date, either for sorting by (-t) or
displaying (-l) the time.
If you are not sure the name of a file you just worked on, you can find it with the
command ls -ltr which sorts by mtime in reverse order, leaving the newest files at the end of the list.