1 xz is a command line tool with syntax similar to that of gzip. 2  xzdec is a decompression-only tool smaller than the full-featured xz tool. 3  A set of shell scripts (xzgrep, xzdiff, etc.) have been adapted from gzip to ease viewing, grepping, and comparing compressed files.
Epoch (astronomy), a moment in time used as a reference for the orbital elements of a celestial body. Epoch (cosmology) or cosmologic epoch, a phase in the development of the universe since the Big Bang. Epoch (geology) or geologic epoch, a span of time smaller than a period and larger than an age.
Like epoch, in English it originally meant the starting point of an age; meaning system of chronological notation is c.1640s; that of historical period is from 1741, e.g. the U.S. Era of Good Feeling (which was anything but) in reference to the Monroe Administration (1817-24), attested from 1817.