There really isn't a difference between all-in-one and multifunction printers at the core. In terms of functionality, both machines offer printing, copying, and scanning, and many allow you to fax as well. The difference typically comes down to the environment where the device is designed to be used, as well as cost and size.  All-in-one devices are geared toward the general consumer and are suited for home use. As a result, they are usually smaller and capable of sitting on a desk. On the other hand, multifunction printers are typically larger machines meant for business and office settings. They are usually large, floor-standing devices and can get very pricey compared to consumer models.