Convert timestamp to date

Monday 21st May 2012 @ 0:26:00am GMT
21/5/2012, 0:26:00am(d/m/y)
5/21/2012, 0:26:00am(m/d/y)
2012-05-21T00:26:00+00:00(ISO 8601)
Mon, 21 May 2012 00:26:00 +0000(RFC 2822)

Unix time, or POSIX time, is a system for describing points in time, defined as the number of seconds elapsed since midnight Coordinated Universal Time (UTC) of January 1, 1970, not counting leap seconds. It is used widely, not only in Unix-like operating systems, but also in many other computing systems and file formats. It is neither a linear representation of time nor a true representation of UTC (though it is frequently mistaken for both), as it cannot unambiguously represent UTC leap seconds (e.g. December 31, 1998 23:59:60), although otherwise the times it represents are UTC. Unix time may be checked on some Unix systems by typing date +%s on the command line. More about timestamps.

Also convert dates to timestamps at datetotimestamp.com