Using Ubuntu Linux/Glossary

Compiz
A compositing window manager.
X11
A bitmap system for displays. Developed by the X.Org Foundation.
Desktop environment
A graphical user interface paired with a set of software.
PulseAudio
Sound server software.
ALSA
Sound architecture.
Advanced Package Tool (APT)
A package management system that originated in Debian (and was also used by Ubuntu since its early days).

See also edit