This article explains how to use the Header of RadTextBox.
RadTextBox is able to display a header above the textbox itself. To define a header for the RadTextBox control, you can use the Header property. It is of type object, so you can assign everything to it - string, UIElement, UserControl, etc.
Here is an example:
<telerikPrimitives:RadTextBox ActionButtonVisibility="Visible" Header="Name"/>
And here is the result:
You can also bind the Header of the RadTextBox control to a data object and use the HeaderTemplate property to define a DataTemplate to visualize the object. You can also change the style of the header with the HeaderStyle property. It can be used to change the foreground of the header for example. When you define a new style, you will have to set the TargetType to ContentControl.