source output impedance: the actual impedance of the output circuit. The output impedance of a device determines just how much current it can provide to a load.
source load impedance: the impedance that the source circuit is designed to serve as a load. This is usually the figure given in the specifications, e.g., the impedance value that the equipment was designed to be connected to.
load input impedance: the impedance that the load is designed to be fed from. As long as this value is higher than the source output impedance, the rest doesnít matter. For example, if a tape recorder is connected to a mixer, this value is the impedance that the recorder wants to serve at its input.
load termination impedance: the actual impedance of the input circuit.