The Unix epoch is the reference point from which Unix time is measured: 1970-01-01 00:00:00 UTC. A Unix timestamp is the count of seconds that have elapsed since that moment. Values before the epoch are negative, while values after it are positive. This simple number-line model gives software a consistent way to compare events without storing a timezone in every value.
Epoch time is also called POSIX time or Unix time. It appears in operating systems, programming languages, databases, APIs, logs, file metadata, and authentication systems. The underlying value represents an instant, not a human display. When an application shows a local date, it applies a timezone and formatting rules to the epoch value. That is why two people may see different clock text while still referring to the same event.
Understanding the Unix epoch makes timestamp debugging much easier. If a value is around 1.7 billion, it is probably current epoch seconds. If it is around 1.7 trillion, it is probably milliseconds. When a date appears thousands of years in the future, the unit was likely interpreted incorrectly. Use the converter linked on this page to test a value and compare local time with UTC before changing your data.
Why 1970?
Unix was developed around this reference date, and the convention became widely adopted by Unix-like systems. The date is not a claim that time began in 1970; it is simply a shared origin chosen for a practical numeric representation.
Epoch time is not a timezone
Epoch time is an elapsed count anchored to UTC. It does not become local time until software renders it. For storage and interchange, keep the numeric value or an explicit UTC representation. For people, format the same instant in the timezone they understand.