According to Wiki: https://en.wikipedia.org/wiki/Graphics_processing_unit#GPU_forms there are different forms of GPU's. Dedicated and external are amongst the different forms. According to this SuperUser answer: What's the difference between graphics solutions and a graphics processing unit? "GPUs that get their data i/O from various ports like USB and even PCI/PCI-E ports that are accessible ports on most laptops". With that said, a dedicated graphics card is plugged into the PCI / PCI-E slot on the motherboard right? So does that mean a dedicated GPU is an external one?
Think of it like a hard drive. You can install your OS on an internal hard drive and you can on an external. The external GPU just allows you to give a computer that would normally be unable to have one or several a GPU or an array of GPUs.
A dedicated graphics card can be either an internal or external card. If it is installed in the PCI Express slot of a motherboard inside a typical computer case then it is an internal "dedicated" or "discrete" card that obtains power from the PCI Express slot and by a cable from the power supply if necessary. If it is connected to a laptop by the USB port or external PCI Express connector then it is an external "dedicated" or "discrete" card which requires a case and power supply of its own, as well as a cooling solution. In either case it is not an "integrated" GPU because it is not soldered to the motherboard, internal to the chipset or internal to the CPU package (case) or die (the actual CPU chip itself.)