1. a symbol the home package of which is the KEYWORDpackage.
2. any symbol, usually but not necessarily in the KEYWORDpackage,
that is used as an identifying marker in keyword-style argument passing.
See lambda (Symbol).
3. Idiom. a lambda list keyword.
keyword parametern.
A parameter for which a corresponding keyword argument
is optional. (There is no such thing as a required keyword argument.)
If the argument is not supplied, a default value is used.
See also supplied-p parameter.
keyword/value pairn.
two successive elements (a keyword and a value,
respectively) of a property list.