Ellipsoid definitions in the coordinate system definition file have the following format
code description semi_major_axis reciprocal_flatteningwhere
code is an identifier for the ellipsoid. This may contain letters, numbers, and the underscore character. It cannot contain blanks.
description is a quoted text description of the ellipsoid
semi_major_axis is the length of the semi-major axis in metres
reciprocal_flattening is the reciprocal of the flattening
Here is an example of the ellipsoid definition section
[ellipsoids]
INTERNATIONAL "International ellipsoid" 6378388.0 297.0
WGS84 "WGS84 ellipsoid" 6378137 298.257223563