A combo box is a commonly used graphical user interfacewidget (or control). Traditionally, it is a combination of a drop-down list or list box and a single-line editable textbox, allowing the user to either type a value directly into the control or choose from a list of existing options by scrolling. Today, the original distinction between a combo box and a drop-down list has often disappeared.
Combo boxes are typically applied to provide autocomplete or autotype functionality in a convenient way to the user.
The term "combo box" is sometimes used to mean "drop-down list". In both Java and .NET, "combo box" is not a synonym for "drop-down list". Definition of "drop down list" is sometimes clarified with terms such as "non-editable combo box" (or something similar) to distinguish it from "combo box".