The machine ID is a key which is unique to your machine, and it is based on a number of issues on your machine. For example will the operating system version and network card etc. be components in this id. If one or more of these components change, the machine id will also change.
The machine id is located in the Registration Information dialog box, and looks like this:
Voith's CODE use the machine id to lock the licence for special licences types to one machine. In other words, the licence can't be moved from one machine to another. If your licence type require usage of the machine id, you will be informed about that in the registration code e-mail from Voith's CODE.