pop-up

Don’t use as a noun. For example, don't use a pop-up; use a pop-up window instead.

Don't use pop up or pops up as a verb to describe the appearance of a window. Use open or a similar verb instead.

It’s OK to use pop-up window to refer to windows that pop up in Help. Don’t use pop-up window as a synonym for dialog.

It’s OK to use pop-up menu for a programming audience to describe the menu that appears when a customer right-clicks an item. If you must use a term to describe this type of menu in content for a general audience, use shortcut menu.

Examples
Answer the questions in the wizard as they appear.
Some commands carry out an action immediately. Others open a dialog so that you can select options.
A pop-up window gives additional information about an option.
If you want to print the information in a pop-up window, right-click the window, and then select Print Topic.
In the pop-up list, select Microsoft Excel.

See also context menu, shortcut, shortcut menu