Masters are collections of widgets designed by you that can be used on wireframes just like single widgets. The advantage of using masters is that when they are edited, the changes are reflected everywhere the master has been used.
Masters can be created for commonly used collections such as a login panel that appears on multiple pages or headers and footers.
When a master is added to a wireframe, it will have a pink mask applied to indicate that the widgets are contained in a master. The mask can be turned off using Wireframe->Mask Masters.
You can right-click and select Master->Place in Background to send the master to the back and lock it into position like templates. This will give them a grey mask.
The default behavior of a master can be set to place in background by right-clicking a master in the Masters pane and selecting Behavior->Place in Background.
In addition, Masters can be set to behave as a Custom Widget by right-clicking a master in the Masters pane and selecting Behavior->Custom Widget.
Masters can used on other masters making them an even more powerful tool for creating and updating designs.