Could someone explain to me what the differences between these are Amp Heads, Amp Stacks, Combo Amps, Guitar Preamps, and Power Amps. I'm not a n00b so to speak just have only had a little piece of **** amp forever and I've never had to deal with this stuff but an amp upgrade is much needed so I'd like to know what all these terms are.

An amp head is a amplification unit containing the preamp, power amp, and transistors which drive the cab's speakers to produce sound.

A Half stack is an amp head connected to an amp cab.
2 amp cabs connected to an amp head would be a full stack.

A combo amp is when the head and cab are built into one unit.

A preamp is where your inaudible guitar frequencies are brought to an audible line level, this is where distortion comes from.

A power amp prepares the signals from the preamp to be driven into the power amp.