There are some terminology which is used through thte documentation, and it is strictly related to astronomical image processing techniques, and implementation details.

A light source, often used to name stars and galaxies in images.
covariance matrix
The matrix \(C\) formed such as \(C_{ij} = <o_i, o_j>\), where \(<,>\) is the inner product operator, and each \(o_i\) is an observation.