Instrument landing system localizer
An instrument landing system localizer, or simply localizer (LOC, or LLZ prior to 2007), is a system of horizontal guidance in the instrument landing system, which is used to guide aircraft along the axis of the runway. == Principle of operation == In aviation, a localizer is the lateral component of the instrument landing system (ILS).
Source: Wikipedia — Instrument landing system localizer (CC BY-SA 4.0)