symbol-name

(symbol-name symbol)

Returns the symbol's name as a string. The reader upcases unescaped symbols like Common Lisp (see the reader case guide), so a symbol reports its upcased name — (symbol-name 'foo) is "FOO" and (symbol-name 'car) is "CAR", the Common Lisp answer. A keyword's leading :, a gensym/make-symbol result's #: prefix and a package qualifier are all where the symbol lives rather than part of its name, and are stripped — the same text princ prints (prin1 keeps them). nil and t are the symbols NIL and T, so they name themselves upcased like any other symbol.

On the compiled backends (JVM/WASM) symbol-name shares the princ-to-string machinery, so a non-symbol argument yields its display text instead of signaling an error (the interpreter signals).

The reader supports the Common Lisp escape syntaxes for symbol names: a backslash makes the next character part of the name verbatim, and a |...| multiple escape makes everything between the pipes part of the name — whitespace and terminating characters included — so '|when used| is one symbol named "when used" and '|Foo| keeps its mixed case.