See the current Perl documentation for time.
Here is our local, out-dated (pre-5.6) version:
time - return number of seconds since 1970
Returns the number of non-leap seconds since whatever time the system considers to be the epoch (that's 00:00:00, January 1, 1904 for MacOS, and 00:00:00 UTC, January 1, 1970 for most other systems). Suitable for feeding to gmtime() and localtime().