The Unix Epoch is a different and unique way to represent dates.
This way of representing dates counts the seconds passed since the 1st of January 1970 at 00:00:00 in UTC (Greenwich timezone)
This date can be possitive (for dates after 1970-1-1) or negative (for dates before 1970-1-1).
The most interesting about this way of representing dates, is that dates are, for the first time, turned into numbers.
Because it counts seconds since a very specific date, this way of representing dates is unique.
The "normal" way of representing dates is unique in a strange way, since there are various time zones and the same date represents different dates in different countries.
|252234223||Thu, 29 Dec 1977 10:03:43 +0100|
|1108486591||Tue, 15 Feb 2005 17:56:31 +0100|
|1101453443||Fri, 26 Nov 2004 08:17:23 +0100|
|0||Thu, 01 Jan 1970 01:00:00 +0100|
|-234234234||Mon, 30 Jul 1962 23:56:06 +0100|
|-1954864745||Tue, 21 Jan 1908 06:00:55 +0100|
It was defined as a 4-bytes integer, so it handles dates from 1901 to 2038 only. Nowadays it is being decided to move it to an 8 bytes integer, so it will be able to handle all the dates through the whole universe's life.