Undefined

Undefined may refer to:

Mathematics

 * Undefined (mathematics), with several related meanings
 * Indeterminate form, in calculus

Computing

 * Undefined behavior, computer code whose behavior is not specified under certain conditions
 * Undefined value, a condition where an expression does not have a correct value
 * Undefined variable
 * Undefined, a function or variable lacking a declaration
 * Undefined, a variable lacking initialization
 * Undefined, an unavailable linker symbol (function, or global variable)

Other uses

 * Undefined, something that lacks any definition
 * Undefined citizenship, a post-Soviet form of statelessness in Estonia