Definition - CAT I
ILS, MLS, GLS, PAR or SBAS with DH not lower than 200ft and an RVR not less than 550m
Definition - CAT II
An ILS or MLS with a DH lower than 200 ft but not lower than 100ft and RVR not less than 300m
Definition - CAT IIIA
An ILS or MLS with DH lower than 100ft and an RVR not less than 200m
Definition - CAT IIIB
An ILS or MLS with DH lower than 100ft or no DH and an RVR lower than 200m but not less than 75m