An A/V receiver has a pre-amp/processor, amplifiers, and possibly a radio tuner in one box.
An A/V pre-amp/processor process information sent by the source (DVD player, CD player, etc), and controls adjustments such as volume, and source selection. It processes and decodes information like Dolby Digital, 5.1, 6.1, etc. These do not have any amplification in them.
An A/V amp amplifies the signal sent by the pre-amp/processor. It can have from 1 to however many channels as you need. Each channel is esentially a line to a speaker. These do not perform any pre-amp/processor duties.
Also, an integrated amp is more or less a receiver without a radio tuner built in.
"Also, an integrated amp is more or less a receiver without a radio tuner built in."
Well, I wouldn't say that. It doesn't do any signal processing, and receivers generally have at least 5 channels of amplification, whereas integrateds have two. On top of that, receivers incorporate a DAC, while integrated amps do not.
Good point Josh. When I wrote that I was thinking a 2 channel receiver minus most gadgets and a tuner.
Their are a select few integrateds that have multichannel amps. Pathos makes one. Also, some newer integrateds have an internal DAC option. The Naim SuperNait and Bryston B100 SST have these. But these really are the rare few exceptions.
A/V Processor: A processing preamplifier. It has all theusual inputs one would expect but its outputs are only line level to feed into a set of power amplifiers. These can be separate stereo or mono amplifiers or they can be multichannel amplifiers with 3, 5 or 7 channels.
A/V Amplifier: An integrated A/V Processor and 5 or 7 power amplifiers. It has all the usual inputs one expects as well as power amplification so its outputs have to include speaker level connections. Very often these devices also have line level outputs for extra power amplifiers as an upgrade option.
A/V Receiver: An A/V Amplifier with a built-in tuner (radio).