What is the difference between a Regenerative and a Superregenerative receiver?
Regenerative receiver uses deliberate positive feedback (called "regeneration") to increase the gain of the RF amplifier. A useful side-effect is to sharpen the tuning (useful search term : Q multiplier).

This regeneration is adjustable; the art of tuning a regenerative receiver for a weak station is to get the positive feedback as high as possible without allowing oscillation to start.

As the BBC Handbook (1928) says...





The super-regen, on the other hand, allows the oscillation to start, but "quenches" it at a frequency above the desired channel bandwidth (above the 5kHz or so audio bandwidth of an AM radio.)

Received RF energy helps the oscillation to start earlier, and build up faster to a high amplitude before the quenching happens, so the effect is to give a super-regenerative receiver enormously high gain and sensitivity. 

However it cannot distinguish between tiny signals on the tuned frequency or larger ones slightly off station, so this sensitivity comes at some cost in interference rejection.