A chip amp is a self contained amplifier on a single integrated circuit, like this:
You just supply power, heatsink, signals in and out and you have tunes. They are cheap and high quality sound. They are intended for car audio, and low priced consumer products like $129 receivers. These days you see them in $400 receivers. But the newer generation chips are excellent quality.
Chip amps can be linear class AB, or they can be class D, like those made by Tripath.
See it is still an integrated circuit, an amp on a chip.
Chip being the slang for a single small square piece of silicon cut from a round silicon wafer with all the discreet components printed right onto the silicon. Resistors, conductors, transistors, caps? all formed onto the silicon. Then the silicon chip is installed in a plastic jacket and connected to the pins with small copper/gold wires.
http://en.wikipedia.org/wiki/Integrated_circuitSee the separate chips formed on the big round wafer. The chips will be cut from the wafer with a diamond saw and assembled into the package. The wafer is about 7" across. These are probably microprocessor chips with millions of discreet parts printed on each square.
I think there are some other classD integrated circuits now besides Tripath, but they were the first. Tripath is out of business now.
The opposite of integrated circuit is a discreet circuit. That means that it is built out of discreet parts instead of all the parts printed together on one piece of silicon. Discreet parts are what you normally think of as resistor or cap, or transistor. In a discreet transistor there is still a piece of silicon inside the package, connected to the pins with wires. But there is only one, and usually nothing else. There are some transistor products that have temp sensors and other cool goodies in there now.
Most class D amplifiers are discreet. This allows using much more powerful transistors and getting much more output power than an IC. A discreet class D amp looks like this:
You can see the discreet transistors bolted to the blue heat sink. There is an opamp input stage, which is an IC, but the output stage is discreet. This bad boy makes 700W into 4ohms, using only 3 pairs of small plastic transistors, with the lowest output impedance of any amp topology, <.001 ohm. And it fits in the palm of your hand.
The last thing is that a class D amp is not a digital amp. It is an analog switching amp. It pulses current into an inductor based on the comparison of the input and output signals. If the output voltage is too low it gives a few pulse of "ON" to catch up. Class D amps are literally a big feedback loop on steroids. A digital amplifier is one that accepts a streaming digital audio signal on it's input, and the DAC is actually the output stage of the amplifier. You can see this topology in Tact amplifiers and the new NAD M2 "direct digital" amplifier, aka power dacs. I wonder if the little Wadia iPod doc power amp is a direct digital amp? Most of the digital amps we talk about these days are class D, analog switching amplifiers. Digital Amp Company, Bel Canto, W4S, B&O modules, Hypex, Spectron, Nuforce, Tripath, etc. They take an analog signal in and spit out an analog signal. the signal is never converted to logic bits. You can picture it as the input signal is being redrawn by the output stage using dots not a smooth line, using ~500,000 dots per second. Then the dots are followed by an analog filter (always with an inductor) which connects the dots. The output filter is what makes or breaks the class D amp, how smoothly can the dots be reconnected. This is Red Wine's success with Tripath chips, Vinnie found a nice recipe for output filter.