(1) (Multiple Document Interface) A Windows function that allows an application to display and lets the user work with more than one document at the same time. If the application is not programmed for MDI and you want to work with multiple documents of the same type concurrently, you must load the application again for each subsequent document. Contrast with SDI.

(2) (Manual Data Input) Refers to entering data using the keyboard rather than by disk, tape or communications link.

(3) See MDI port.