Header

Here is a typical geo format file header from a .geo file:

PGEOMETRY V5
NPoints 80 NPrims 12
NPointGroups 0 NPrimGroups 0
NPointAttrib 0 NVertexAttrib 0 NPrimAttrib 0 NAttrib 0

The first line tells us that this is version 5 of the geometry format.

NPoints: The number of points in our file.
NPrims: The number of primitives (e.g. polygons, nurbs patches, meshes, etc.)
NPointGroups: The number of point groups.
NPrimGroups: The number of primitive groups
NPointAttrib: The quantity of point attributes per point
NVertexAttrib: How many attributes per vertex.
NPrimAttrib: The number of attributes for each primitive
NAttrib: Also known as 'detail' attributes, these are global attributes related to the entire geometry, not to any particular aspect.

Obviously, this was a pretty simple geometry! Here's a more complicated one:

PGEOMETRY V5
NPoints 226 NPrims 84
NPointGroups 1 NPrimGroups 1
NPointAttrib 3 NVertexAttrib 1 NPrimAttrib 1 NAttrib 2

If you want to see what's actually in this file, read on in the point attributes section.