Scope

In computer programming, the scope of a variable refers to where and when in the program that variable can be accessed and/or modified. It is considered good programming practice to make variables as narrow a scope as feasible so that different parts of your program do not accidentally interact with each other by modifying each other's variables. Common techniques for doing so are to have different sections of your program use different namespaces[?], or else make individual variables private through either dynamic variable scoping or lexical variable scoping.

Also the term used in firearms for a telescopic sight.