ControlTipText Property [Access 2003 VBA Language Reference]
You can use the ControlTipText property to specify the text that appears in a ScreenTip when you hold the mouse pointer over a control. Read/write String.
expression Required. An expression that returns one of the objects in the Applies To list.
You set the ControlTipText property by using a string expression up to 255 characters long.
For controls on forms, you can set the default for this property by using the default control style or the DefaultControl property in Visual Basic.
You can set the ControlTipText property in any view.
The ControlTipText property provides an easy way to provide helpful information about controls on a form.
There are other ways to provide information about a form or a control on a form. You can use the StatusBarText property to display information in the status bar about a control. To provide more extensive help for a form or control, use the HelpFile and HelpContextID properties.