Definitions for "Modeless"
Non-restrictive or non-limited interaction. Modeless often describes a secondary window that does not restrict a user's interaction with other windows. Compare modal.
(as contrasted to modal modeless form is one that allows you to go away and come back to it. You do not have to close a modeless form to deactivate it, and you can access the main menu while the form is active.
A DialogBox that does not limit your interaction with the rest of an application.