Let you visitors know when your page was last modified. In this example, first it is defined how time and date must be display (first line in bold), and then it is included the "LAST_MODIFIED" information.
 

Here's what it looks like:
 

Page last modified on 01/25/2010

You will find bellow additional code and its description. They may be used in the first bold line in the example in order to modify how the time related variables are displayed.
 

Code	Description
%a	abbreviated weekday name
%A	full weekday name
%b	abbreviated month name
%B	full month name
%c	locale's appropriate date and time
%C	default date and time format
%d	day of month - 01 to 31
%D	date as %m/%d/%y
%e	day of month - 1 to 31
%h	abbreviated month name (alias for %b)
%H	hour - 00 to 23
%I	hour - 01 to 12
%j	day of year - 001 to 366
%m	month of year - 01 to 12
%M	minute - 00 to 59
%n	insert a newline character
%p	string containing AM or PM
%r	time as %I:%M:%S %p
%R	time as %H:%M
%S	second - 00 to 61
%t	insert a tab character
%T	time as %H:%M:%S
%U	week number of year - 00 to 53
%w	day of week - Sunday=0
%W	week number of year - 00 to 53
%x	Country-specific date format
%X	Country-specific time format
%y	2 digit year - YY
%Y	4 digit year - YYYY
%Z	timezone name