Questions
What is a Unix timestamp?
The number of seconds since 00:00:00 UTC on January 1, 1970 (the Unix epoch), not counting leap seconds. It's the same everywhere in the world at a given moment.
What is the year 2038 problem?
Systems that store Unix time as a signed 32-bit number overflow on January 19, 2038 at 03:14:07 UTC. Modern systems use 64-bit values instead.