defpackage

(defpackage name (:use package...) (:export symbol...) (:nicknames name...) (:import-from package symbol...))

Defines a new package named name and returns the name symbol. Like in-package, it is a literal, top-level directive consumed at read/compile time, so packages are defined in source order. The name and the clause arguments are keywords, bare symbols, strings, or uninterned symbols (:mypkg, mypkg, "mypkg", #:mypkg — the last is the portable defpackage idiom).

• (:use package...) makes the external (exported) symbols of the listed packages visible unqualified. The used packages must already exist. Without a :use clause nothing is visible unqualified — write (:use :cl) to use the standard symbols without a cl: prefix. common-lisp and common-lisp-user are built-in nicknames for cl and cl-user, so (:use #:common-lisp) works too.
• (:export symbol...) declares the package's external symbols: they are reachable as name:symbol from other packages, and inherited by packages that use this one. Symbols interned later (for example defuns made under (in-package name) that are not in the :export clause) are internal and require the double colon, name::symbol.
• (:nicknames name...) registers alternate names for the package; a nickname resolves everywhere the canonical name does. A nickname that collides with an existing package (or nickname) is an error.
• (:import-from package symbol...) makes the named symbols of package visible unqualified without using the whole package. Resolution is textual: an imported name resolves to the source package's canonical spelling, so (:import-from #:common-lisp #:car) gives a use-nothing package just car.
• (:documentation "...") and (:size n) are accepted and ignored.

Redefining an existing package is an error, and so are :shadow/:shadowing-import-from (rontolisp has no symbol shadowing) and any other clause (:intern, ...). See Packages for the full rules.