Amateur radio operators have quite the collection of standard (de facto or otherwise) abbreviations - 'Q' signals describes a group of them that is quite common. They are used for brevity and clarity. QRP means to 'reduce power' and the term has been applied to transmitting with 5 watts (I may be off here) or less power. In the strictest sense, QRP does not apply to the reciever. With that said, there is a desire among some low power (or QRP) operators to use equipment that is compact and/or consumes the least amount of power. That may be to allow portability or emergency operation for long periods of time. Quite often receivers that are paired with low power (QRP) transmitters are given the name QRP receiver. Quite often, QRP equipment is simpler but performs admirably allowing home construction with modest levels of skill.
ARRL and RGSB as well as numerous QRP groups have websites and publications with plenty of information.