PCB (Printed Circuit Board) is a motherboard made of an insulating material, such as fiberglass. The individual electronic components are laminated onto the surface and connected by conductive tracks.
A motherboard connector designed for connecting processors. It is rectangular in shape and its name often indicates the number of conductors.
A HTPC case (Home Theater Personal Computer) is a case for PCs optimised for watching movies and TV programmes. People usually place them in the living room and connect to a TV. They are often supplied with a remote control for extra convenience.
Slots are interfaces for connecting harware such as a processor, expansion cards, graphics cards, special modules, etc.
A chassis is a PC case with prepared holes for all computer components.