Glossary is usually defined as an alphabetical list of technical terms in some specialized field of knowledge. This knowledge gallery glossary provides a collection of knowledge gallery documents that define many technical terms. These terms are arranged alphabetically, but you can quickly jump to a specific term by selecting its first letter from the index of the knowledge gallery glossary below.

The Universe is defined as the summation of all particles and energy that exist and the space-time in which all events occur. Based on observations of the portion of the Universe that is observable, physicists attempt to describe the whole of space-time, including all matter and energy and events which occur, as a single system corresponding to a mathematical model.