Acronym for Advanced Linux Sound Architecture.

Unofficial wiki:

The Advanced Linux Sound Architecture (ALSA) provides audio and MIDI functionality to the Linux operating system. ALSA has the following significant features:

  1. Efficient support for all types of audio interfaces, from consumer soundcards to professional multichannel audio interfaces.
  2. Fully modularized sound drivers.
  3. SMP and thread-safe design.
  4. User space library (alsa-lib) to simplify application programming and provide higher level functionality.
  5. Support for the older OSS API, providing binary compatibility for most OSS programs.

ALSA is superceding the OSS api as the sound driver set for the LinuxKernel in 2.6.