A combo box is a user interface control GUI element. It is a combination of a drop-down list or list box and a single-line textbox, allowing the user either to type a value directly into the control or choose from the list of existing options. An example of this use is the address bar of graphical web browsers. 
** http://en.wikipedia.org/wiki/Combo_box

It can be used to represent a ToOneRelationship in the model

''EditHint: I'm not sure this and similar "widget" topics belongs in WikiWiki. WikiIsNotaDictionary''

Perhaps... but I want to start a discussion on how WidgetsRepresentRelationshipsInTheModel... and for that, I might need this page (with clear extendable definitions of the features of each widget)... please wait before moving this and other widget definitions to WikiWiki --LuxSpes

''A ComboBox is a Gui Programming Construct, not a '''word'''. What is described on this page is not a word definition, but a ProgrammingArtifactDescription. This wiki is full of such descriptions. -- DonaldNoyes 20110520''