A Gaussian grid is used in the earth sciences as a gridded horizontal coordinate system for scientific modeling on a sphere (i.e., the approximate shape of the Earth). The grid is rectangular, with a set number of orthogonal coordinates (usually latitude and longitude).
The gridpoints along the longitudes are equally spaced, while they are unequally spaced along the latitudes, where they are defined by their Gaussian quadrature. There are no grid points at the poles.
In a regular Gaussian grid, the number of gridpoints along the longitudes is constant, usually double the number along the latitudes.
In a reduced (or thinned) Gaussian grid, the number of gridpoints in the rows decreases towards the poles, which keeps the gridpoint separation approximately constant across the sphere.