Here is the VERY simple version:
Amplifier: takes a variable-level signal from a pre-amp and drives your speakers (or headphones).
Preamp: takes line-level signals from components and sends them to the amp as a variable-level signal (so you can adjust the volume). Most preamps allow you to hook up multiple line-level signals and switch between them.
Tuner: a component that receives radio broadcasts and outputs them as a line-level signal to a pre-amp.
OK, those are the components at their most basic... when you put them together:
Integrated amplifier: a single component that includs BOTH a preamp and an amplifier.
Reciever: a single component that contains a tuner, preamp, and amp.
AV receiver: truth is this could be anything LOL. But it is normal a receiver with some kind of "multi-channel" processor and outputs to drive 4 or more speakers.