Thermally Advantaged Chassis

A Thermally Advantaged Chassis (TAC) is a computer enclosure that complies with the Thermally Advantaged Chassis specifications created by Intel. It is capable of maintaining an internal ambient temperature below 38 degrees Celsius when functioning with Intel's Pentium 4 and Celeron D processors based on 90 nm process technology, and an ambient temperature below 39 degrees Celsius when using a Pentium D processor.

Source: Wikipedia — Thermally Advantaged Chassis (CC BY-SA 4.0)