Lindworm in British heraldry

Heraldry

Heraldry is the profession, study, or art of creating, granting, and blazoning arms and ruling on questions of rank or protocol, as exercised by an officer of arms. Heraldry comes from Anglo-Norman herald, from the Germanic compound harja-waldaz, "army commander"...

, is a technical term for a wingless bipedal dragon

Dragon

A dragon is a legendary creature, typically with serpentine or reptilian traits, that feature in the myths of many cultures. There are two distinct cultural traditions of dragons: the European dragon, derived from European folk traditions and ultimately related to Greek and Middle Eastern...

 often with a venomous bite.
In modern Scandinavian languages, the cognate lindorm can refer to any 'serpent' or monstrous snake, but in Norwegian heraldry, it is also a technical term for a 'seaserpent' (sjøorm), although it may also stand for a 'lindworm' in British heraldry.

Generally, the word lindworm stood for the Latin word draco (whence Norse dreki), thus could refer to any draconic creature, from a real life constrictor snake to a legendary dragon.