Complex sentence: In aviation, a localizer (LOC) is the lateral component of the instrument landing system (ILS) for the runway centreline when combined with the vertical glide slope, not to be confused with a locator, although both are parts of aviation navigation systems.
Split into simpler sentences: In aviation, a localizer (LOC) is the lateral component of the instrument landing system (ILS) for the runway centreline when combined with the vertical glide slope. It is "not" to be confused with a locator, although both are parts of aviation navigation systems.