If the signals of two repeater transmitters mix together in one or both of their final amplifiers and unwanted signals at the sum and difference frequencies of the original signals are generated and radiated, what is this called?

When two or more strong signals mix in a non-linear component (like a final amplifier stage) and produce unwanted spurious signals at their sum and difference frequencies, this phenomenon is called intermodulation (or "intermod"). These newly created signals can be radiated out and interfere with other receivers tuned to those sum and difference frequencies. This is a highly common issue at shared radio sites with multiple repeater transmitters operating simultaneously. The distractors refer to entirely different concepts: neutralization prevents unwanted self-oscillation in an amplifier, amplifier desensitization refers to receiver overload from a strong nearby signal, and adjacent channel interference is caused by signals spilling over rather than mixing to create new frequencies.