All words have associated definition Quotations. A word's definition quotation is called when the word is executed. A colon definition is a word where this quotation is supplied directly by the user. This is the simplest and most common type of word definition.

Defining words at parse time:

:

; ( -- * )

Defining words at run time:

define ( word def -- )

define-declared ( word def effect -- )

define-inline ( word def effect -- )

Word definitions must declare their stack effect. See Stack effect declarations.

All other types of word definitions, such as Symbols and Generic words and methods, are just special cases of the above.