unit in stratigraphy
A stage or age in geology is a period of time measured in millions of years. It is less than an epoch, and more than a chron or chronozone.
Technically, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions of years of sedimentation or deposition. An example of a stage in the Geologic time scale is the Kimmeridgian.