Tool Tip
From SmartWiki
When creating a Custom Field, the Tool Tip field allows you to specify "mouse-over" help.
When editing a record if the user hovers their mouse pointer over the relevant custom field, the text in the Tool Tip section will appear:
Tool Tip is equivalent to the Instruction section on Standard Fields
Note: the length of time that a tool tip is displayed is a property of the Browser and cannot be modified.