S0: The number of sectors (excluding non-geographic sectors) for which there are no valid postcodes in OSM. So if s0=0, every sector has at least one unit appearing at least once in OSM.
S5: The number of sectors (excluding non-geographic sectors) for which fewer then 5% of the geographic units appear on at least one object in OSM. So if s5=0, then every sector has at least 5% of its geographic units appearing at least once in OSM.
Units: The total number of units (individual postcodes) listed in Code-Point Open
Geo. Units: An estimate of the number of geographic units, computed as follows: The number of postal units which either exist in OSM or have fewer than 5 or more other units with the same coordinates in Code-Point Open. This is designed to exclude PO Box units that are located at Royal Mail Delivery Offices.
Mapped: The number of unique valid units appearing as an addr:postcode value in OSM.
%: OSM progress towards mapping at least one example of each unit, measured against the number of geographic units.