This is a physics concept from electromagnetism. The magnetic scalar potential is a mathematical function used to describe magnetic fields in regions where there are no electric currents or changing electric fields — that's what "outside sources" means.

In these source-free regions, you can describe the magnetic field using a scalar potential (simpler math) instead of the full vector potential. It's useful for solving problems like magnetic fields around permanent magnets or in empty space between current-carrying wires.

Think of it like gravitational potential energy — a single number at each point that tells you about the field, rather than needing vectors everywhere.