ACPI stands for Advanced Configuration and Power Interface. This is a specification by Toshiba, Intel and Microsoft. Besides many other things it also defines power management. This is why it is often compared to APM.
The ACPI4Linux project has started at the beginning of 1999. The ACPI4Linux project is a kernel driver project aimed at implementing full ACPI support for Linux, including fan control, dock/undock detection and a WindowMaker dockable temperature meter. You may reach it at ACPI4Linux . Also this project provides a survey of ACPI compliant BIOSes .
Linux ACPI-HOWTO by Ariel Glenn. This document describes how to compile, install, and use the ACPI driver for Linux and its associated applications.