Just to clarify things a bit more, I'll quote from the stat(2) man page [1]:

    time_t    st_atime;   /* time of last access */
    time_t    st_mtime;   /* time of last modification */
    time_t    st_ctime;   /* time of last status change */

    The field st_atime is changed by file accesses, for example, by
    execve(2), mknod(2), pipe(2), utime(2) and read(2) (of more than zero
    bytes).  Other routines, like mmap(2), may or may not update
    st_atime.

    The field st_mtime is changed by file modifications, for example, by
    mknod(2), truncate(2), utime(2) and write(2) (of more than zero
    bytes).  Moreover, st_mtime of a directory is changed by the creation
    or deletion of files in that directory.  The st_mtime field is not
    changed for changes in owner, group, hard link count, or mode.

    The field st_ctime is changed by writing or by setting inode
    information (i.e., owner, group, link count, mode, etc.).

[1]: http://man7.org/linux/man-pages/man2/stat.2.html