[This is preliminary documentation and subject to change.]
An object's Description property, retrieved by calling the IAccessible::get_accDescription method, provides a textual description for an object's visual appearance. The description is primarily used to provide greater context for low-vision or blind users, but can also be used for context searching or other applications.
All objects should have a description, except in cases where the description is obvious or redundant based on the object's Name, Role, State, and Value properties. A button with the word "OK" does not need additional description, but all graphical objects and controls must have some.
For example, imagine a toolbar containing a button that shows a picture of a cactus. The button's properties describe its role, name, purpose, and so on, but the Description property conveys information that is less tangible, like "A button that shows a picture of a cactus."
Not all objects support the Description property; if the call to get_accDescription returns the DISP_E_MEMBERNOTFOUND value, then no object description is available.