AIO stands for "All In One" and refers to a liquid CPU cooler that combines the parts necessary to liquid-cool your CPU into a pre-packaged solution that you bolt on in about 20 minutes. An AIO typically includes a water block, radiator, tubes, fans, fittings, and pump into one sleek package. The liquid in an AIO is only the carrier of the heat, and the heat is dissipated by the radiator. AIOs are a form of liquid cooler where the entire cooling solution is pre-packaged and closed off to the point of not requiring or even allowing maintenance. They are often more complex to install than a standard air cooler, but they require very little oversight or maintenance after installation. AIOs are less bulky than traditional air coolers and can look better, but they have more potential points of failure than air coolers. Reputable AIO manufacturers tend to put lengthy warranties on their products, as they are confident in their systems.