Typically, a reciever is a catch-all phrase for an intergrated amplifier that also has a tuner. These days, most recievers are AVRs or Audio Video Recievers. You may also find units referred to as AVRs that do not have tuners but they would be rare.
Without the tuner or other AVR stuff [DTS, Dolby Digital, ect], the unit is usually referred to as an intergrated amplifier. That is that it comes with a pre-amp and amplifier in one box and nothing else.....usually used for audio purposes.
Then there are units that are simply "amplifiers". Here there is no tuner, pre amp, or any of the AVR stuff. They do amplification and nothing else.