A window air conditioner is an air conditioner that contains every working piece of the air conditioner in one box.
The compressor,condenser,evaporator coils and fan motor etc are all contained in one box that you sit in the window and just plug in to get the room cooled down.
A split air conditioner is an air conditioner where you hang one part of the air conditioner inside the house on the wall and the other part goes outside and it's connected through refrigerant lines.
The window air conditioner doesn't need an ac tech to install but a split air conditioner needs an air conditioner tech to install it since it needs a vacuum pulled on the lines to remove contaminates.