A Unix timestamp represents a time as the number of seconds elapsed since January 1, 1970, at 00:00:00 UTC (the Unix epoch). Software uses timestamps to record events, compare dates, and coordinate systems. Some formats use milliseconds or other units, so the unit should be verified when interpreting a value.
In cyber security, timestamps can help analysts order log events and investigate activity. They can also be used to initialize a pseudorandom number generator (PRNG). If a security-sensitive value is generated from a PRNG seeded only with a predictable timestamp, an attacker who can estimate the time may be able to reproduce the sequence. Timestamps are therefore useful for recording when something happened, but they are not a substitute for secure randomness. Systems should use cryptographically secure random generators for keys, tokens, and other secrets.