In computing, lookup usually refers to searching a data structure for an item that satisfies some specified property. (Note that in grammatical usage, lookup is the noun form describing the verb form to look up.) For example, variable lookup performed by a (scripting) language interpreter, virtual machine or other similar engine usually consists of performing certain actions to dynamically find correspondence between variable identifier and actual variable internal representation, usually involving symbol table lookup. Symbol table lookup can be performed either during run-time (interpreter or scripting engine), or during compile time (compiler). A hybrid scheme when lookup is performed both during translation phase and then later during runtime is also possible (e.g. bytecode compiler and virtual machine). In all of these cases, search item is a variable and the search property (or search criterion) is a variable name. Variable lookup is usually performed according to variable visibility rules that are specific to the (scripting) language in question.