Checkout the following notable exampes:
See more notable events in unix time.
It's the number of seconds since the Unix Epoch. The Unix Epoch starts January 1st, 1970 at UTC, and skips leap seconds. The Unix Epoch is based on a UTC starting point, so does not change in different timezones. Read more on wikipedia.
In early 2038 the Unix Time Stamp, if uses 32-bit signed integer, will overflow. This is really bad. Older systems will need to upgrade their timestamp storage to cope to avoid failure. Read more on wikipedia.