Each symbol has a property list on which semi-permanent properties of the symbol can be stored. Each property has a property name or indicator, and a value. Property list values are retrieved and set by two functions:
(get symbol propname)
retrieves the value of the specified
property for the specified symbol. If no such property exists, the value
returned is NIL.
(setf (get symbol propname) value)
sets the value of the specified property for the specified symbol,
displacing any previous value.
Each symbol has a single property list, which appears the same to all parts of a Lisp program and is unaffected by binding.