"This document defines the meaning of commonly used terms which are specific to signalling or used in a signalling context. The objective is to provide a common and clearly understood meaning of each term. This glossary is arranged in alphabetical order. Acronyms are arranged within the alphabetical list. Certain entries cross-reference to another entry, especially where an abbreviation is shown. Title case has been used to draw attention to defined terms. Generally, the full definition is shown only once. Where appropriate, the use of both new and old terminology is included. Level crossings have a large number of specific terms and for this reason their entries have been given a separate section (see section C3). Signal sighting terms are of a specialist nature and therefore a separate section has also been created for these (see section C4). "