The term originally applied to any monastic or monastic-style strong ale. After introduction of an official Trappist beer designation by the International Trappist Association in 1997, it came to mean products similar in style or presentation to monastic beers. In other words, an abbey beer may be:

- produced by a non-Trappist (e.g. Benedictine) monastery
- produced by a commercial brewery under commercial arrangement with an extant monastery
- branded with the name of a defunct or fictitious abbey by a commercial brewer
- given a vaguely monastic branding, without mentioning a specific monastery, by a commercial brewer

Although abbey beers do not conform to rigid brewing styles, most tend to include the most recognisable and distinctive Trappist styles of brune (Belgian brown ale, aka dubbel), strong pale ale or tripel, and blonde ale.