Integrated is a term used to describe when a hardware device is combined into another device. For example, several motherboards have an integrated network card, video card, or sound card. These devices can be disabled and enabled from the CMOS or using a jumper or DIP switch on the motherboard. They may also be automatically disabled when a new card is placed into an expansion slot.
Why are some devices integrated and others are not?
As mentioned above, if a device is part of the motherboard, it is integrated. Many manufacturers integrate the network card, sound card, and sometimes the video card into the motherboard to help reduce the overall cost and size of a computer. Although integration can make a computer cheaper, smaller, and easier to manufacturer, if an integrated device goes bad, it cannot be replaced because it's part of the motherboard.