What is the term for the reduction in receiver sensitivity caused by a strong signal near the received frequency?
Why A strong off-frequency signal can drive the receiver's front end or mixer toward saturation, forcing the AGC down or compressing the stages so that weak desired signals no longer produce normal output. That loss of effective sensitivity in the presence of a nearby strong carrier is called desensitization, or "desense." It is a common problem at repeater sites and in crowded bands, and a sharp preselector or attenuator ahead of the receiver is the usual cure.
Watch out Cross modulation is different: there the modulation of the strong signal is transferred onto the desired signal, so you hear the interfering station's audio rather than just a weaker signal. Reciprocal mixing is noise from a local oscillator's phase noise mixing with a strong adjacent signal, raising the noise floor.
Strong neighbor makes your receiver go deaf = desense. If you hear his audio instead, that's cross modulation.