The highest accuracy approaches are the CAT III approaches that may provide guidance all the way to the runway with no requirement for decision height (CAT IIIB) nor for runway visual range (CAT IIIC).

According to EASA AIR OPS Annex I Definitions for terms used in Annexes II to VIII:

13) ‘category I (CAT I) approach operation’ means a precision instrument approach and landing using an instrument landing system (ILS), microwave landing system (MLS), GLS (ground-based augmented global navigation satellite system (GNSS/GBAS) landing system), precision approach radar (PAR) or GNSS using a satellite-based augmentation system (SBAS) with a decision height (DH) not lower than 200 ft and with a runway visual range (RVR) not less than 550 m for aeroplanes and 500 m for helicopters.

(14) ‘category II (CAT II) operation’ means a precision instrument approach and landing operation using ILS or MLS with:

(a) DH below 200 ft but not lower than 100 ft; and
(b) RVR of not less than 300 m;

(15) ‘category IIIA (CAT IIIA) operation’ means a precision instrument approach and landing operation using ILS or MLS with:

(a) DH lower than 100 ft; and
(b) RVR not less than 200 m;

(16) ‘category IIIB (CAT IIIB) operation’ means a precision instrument approach and landing operation using ILS or MLS with:

(a) DH lower than 100 ft, or no DH; and
(b) RVR lower than 200 m but not less than 75 m;