Common Lisp the Language, 2nd Edition
Every symbol has an associated string called the print name. This string is used as the external representation of the symbol: if the characters in the string are typed in to read (with suitable escape conventions for certain characters), it is interpreted as a reference to that symbol (if it is interned); and if the symbol is printed, print types out the print name. For more information, see the sections on the reader (section 22.1.1) and printer (section 22.1.6).
This returns the print name of the symbol sym. For example:
(symbol-name 'xyz) => "XYZ"
It is an extremely bad idea to modify a string being used as the print name of a symbol. Such a modification may tremendously confuse the function read and the package system.
X3J13 voted in March 1989 (CHARACTER-PROPOSAL) to specify that it is an error to modify a string being used as the print name of a symbol.