The term AIRLINE ABBR. refers to abbreviations used by airlines in the aviation industry. The most common abbreviations are DEP (3 letters) which stands for Departure, ETA (3 letters) which stands for Estimated Time of Arrival, ETD (3 letters) which stands for Estimated Time of Departure, and TWA (3 letters) which stands for Trans World Airlines. These abbreviations are used to help streamline communication between airline personnel and passengers.