An abbreviation was a shorter form of a longer word for the sake of brevity.
The term "troglyte" was an abbreviation of the Earth term troglodyte, meaning "cave dweller". (TOS: "The Cloud Minders")
Some starships had abbreviated nicknames that were used in informal speech and printed on casual duty attire. These included "Voy" (USS Voyager), "Disco" (USS Discovery), and "Ritos" (USS Cerritos). (citation needed • edit)