Unix time is the number of seconds that have elapsed since 00:00:00 UTC on 1 January 1970, minus leap seconds. It is the backbone of timekeeping in computing.
The 2038 Problem
Because many legacy systems store the timestamp as a signed 32-bit integer, they will overflow on January 19, 2038, causing clocks to wrap around to 1901. Converting timestamps accurately and migrating to 64-bit systems is an ongoing global effort.