Internal & External
Hardware refers to the physical components of the computer. This includes the internal parts such as the motherboard, power supply and memory. The cables and the ports on the outside of the case are also hardware along with the monitor, mouse and keyboard.
Desktop computers usually come with the ability to upgrade and change many of the internal components like the RAM memory or the CPU. In addition, the computer may have PCI or PCI-X slots that allow you to add more features. You can install a bluetooth card to wirelessly connect to a speaker or a USB-C port to connect to an external hard drive.
Desktop and laptop computers have similar parts, however, they are different in many ways. Laptops are made to be portable so the hardware tends to be smaller and more compact. Many of the external components are built into the laptop's case such as the monitor and keyboard and there is a track pad that substitutes for a mouse.