The dexterity bonus applied to your armour class can be limited by several
factors, including the armour you are wearing (in a given location) and the
load you are carrying (this limit applies to all armour locations). The "max
dex" entry next to each location armour class indicates the current value of
this limit for your PC.
Example: If your effective dexterity is 15, which would normally grant you a
dexterity bonus of +2 to your armour class, but you are wearing full plate
armguards, which limit your maximum dexterity bonus to +1, your armour class
in that location would only be reduced by one in that location, rather than
two, as a result of your dexterity. Were you wearing lighter armour, it
would be reduced instead by two.