Epoch Time and Unix Time are just different names for the same thing. Also known as POSIX Time.
Greenwich Mean Time (GMT), Greenwich Mean Time is a coordinated world time zone centered in London and ending in Wellington.
Epoch refers to an era of significant events or changes, and is used by systems such as Unix and POSIX to represent the passage of date and time. (00:00:00 UTC on January 1, 1970). That is, 0:00 on January 1, 1970.
Timestamp is said to have originated from the rubber stamps used in the West to indicate the time of sending or receiving mail and other documents. It has a date in the center and a triangle at the top that points to a specific time around a circle representing a 24-hour period.
This stamp was stamped on a piece of paper to mark a specific time, and in the current IT system, it represents the time that has passed based on an epoch.