A package establishes a mapping from names to symbols. At any given time, one package is current. The current package is the one that is the value of *package*. When using the Lisp reader, it is possible to refer to symbols in packages other than the current one through the use of package prefixes in the printed representation of the symbol.
Figure 11–1 lists some defined names that are applicable to packages. Where an operator takes an argument that is either a symbol or a list of symbols, an argument of nil is treated as an empty list of symbols. Any package argument may be either a string, a symbol, or a package. If a symbol is supplied, its name will be used as the package name.