Xdata used to assign extended data to any entity in autocad
For example, If we can assign Pipe Properties to Line Object in AutoCAD
This is really good method to store additional info on any AutoCAD Object
How to use XData Manually on autocad
Use XDATA Command to assign extended data to selected object, you also have to provide Application Name which is used to get data later
Use XDLIST Command to view XData Assign with specific object, you really need to know name of application to view data
XData is generally more suited for attaching to objects. XData is indexed by registered applications (RegApps), so you can assign data for one "application" without interfering with others. There is a limit to the total XData you can assign to any given object but its quite big; if you overrun the limit its a good indication there's a better way to do what you are trying.