It's a module that requires an additional daughterboard (aka carrier board). All of the IO is on the daughter board, that way you're able to precisely customiz

It's a module that requires an additional daughterboard (aka carrier board). All of the IO is on the daughter board, that way you're able to precisely customize what features, IO, etc. the computer has (within the limits of what the SoC/CPU has to offer). The modular approach makes a small hardware manufacturer's life much easier. Manufacturing 10 (just throwing a number out there) hardware product SKUs means you've got to maintain different bills of materials, test jigs, firmware, etc. With a module, you can engineer a module once and sell it many times over. One BoM, one test jig set up, fewer versions of firmware to maintain, etc. You'll find computer on module type systems in a lot of appliances, pieces of large machinery, etc. Situations where you have low to medium volume where it doesn't make sense to design and manufacture a motherboard from the ground up, but you have specific needs for features and IO.