Simplified Common Lisp reference
Symbol class: Functions, Evaluation, Flow Control, Definitions and Syntax
Symbol type: macro
defparameternameinitial-valuedocumentation(optional) => an object
Argument description:
name a name for global variable
initial-value an expression
documentation documentation string

DEFPARAMETER defines global variable with dynamic scoping. Usual conventions dictate to make such variables easy to distinguish so their name is surrounded by stars. Value for variable is reevaluated for each occurence (unlike with DEFVAR). See also DEFVAR, LET, SETQ.

(defparameter *my-global-variable* (+ 3 5)) => *MY-GLOBAL-VARIABLE*
*my-global-variable* => 8
Function indexFull documentation for defparameter (HyperSpec)