Desktop Computers are personal computers that can only be used in a single location on a desk or a table hence the name 'Desktop' Computers. Desktop Computers have no internal source of power so they need to be always plugged-in in order to operate.
The advantage of Desktop Computers is that they can be upgraded. You can increase the RAM, the Internal Storage and Graphics. You cannot increase the Motherboard capabilities but you can replace it if you want for a more powerful Motherboard.
Mini-Tower Desktops are Desktops smaller than Tower Desktops. Mini-Tower Desktops are compact taking a small space on your desk or table.