Although the well-known Windows design actually places the list box below the box showing the single value, most older user interface designs (such as Motif) and current OS/X designs place the list box so that the currently-selected item is at the location of the box, so that you do not need to move the mouse to pick the same value. This was sometimes called a "popup list" or a "choice" or "chooser". However it seems that "drop-down list" is the common term used to describe these widgets nowadays.
A drop-down list differs from a combo box in that the entry portion of a drop-down list cannot be edited. The navigation field of a web browser is an example of a combo box rather than a drop-down list.
A disadvantage of a drop-down list vs. a list box or tabs is that only one option is visible at a time and the user may not recognize the appearance of the control as containing a list of options.
This type of control is called a "Pop-up menu" on the Macintosh platform , however the term "popup menu" is used to refer to Context menus in other GUI systems. The Macintosh also has the notion of "Pop-down menus". The distinction is that, when the menu is closed, a pop-up menu's title shows the last-selected item while a pop-down menu shows a static title like a menu in the menu bar. Thus, the uses are different - popups are used to select a single option from a list while popdowns are used to issue commands or in cases where multiple options can be selected. An interactive live demo example of this type of list can be seen here