A pad or component on a schematic or printed circuit board that facilitates access to a signal for the purpose of measuring or interacting with it.
Test points on a PCB may be as simple as an exposed copper pad (no solder mask) which allows a test probe to contact it. An engineer may also solder wire or a component directly to it if needed. More complex text points may involve a through-hole pad with a loop of wire or some other component that is intended for easy connection.
