General Definition: 1. Two relatively narrow vertical flat surfaces that separate horizontally from each other or any thing or any action that can be associated with this in context. As a Noun: 1. A set of doors that slide open automatically. English = automatic doors. 2. A set of doors that slide open. English = sliding doors. As a Verb or Adjective: 1. Of automatic doors, to open. 2. Of sliding doors, to open.