TPM stands for Third Party Maintenance. You can get "third party" maintenance on any device that you can buy a maintenance contract on. It just means that the original manufacturer or the officially approved service provider isn't providing the maintenance. With a device or service, buyer is assumed to be first party, seller is the second party and in this case the maintainer would be a third party.

The "Maintenance" in TPM is the desire by the end user or operator of the device to keep the device in a state where it can provide its purposeful use or production value for a fixed period of time. For example, when you buy a network switch from a Cisco reseller, you expect that network switch to work for ten years (or more). It may come with a warranty that will assist with or completely provide the maintenance function and the service level replacement that you desire for the device to maintain its function in your estate. Beyond the warranty, however, the function of the device once you become owner is your responsbility. If component parts burn or wear out and you no longer have a warranty entitlement with the seller/manufacturer/service provider, you may have a device that functions badly or no longer functions. You can try and find a replacement part yourself, complain to the seller that the device you were sold five years ago no longer functions or you can replace the device, if you don't have a mantinenance entitlement on the device. Or you can buy a maintenance entitlement for the device from a "third party" provider.