USB devices with similar attributes and services are grouped into device classes. Each device class has a corresponding driver, one for each framework. Devices within a class are managed by the same device driver pair. However, the USB specification also allows for vendor-specific devices that are not part of a specific class.
The Human Interface Device (HID) class contains devices that are user-controlled such as keyboards, mouse devices, and joysticks. The Communication Device class contains devices that connect to a telephone, such as modems or an ISDN interface. Other device classes include the Audio, Monitor, Printer, and Storage Device classes. Each USB device contains descriptors that reflect the class of the device. A device class specifies how its members should behave in configuration and data transfer. You can obtain additional class information from http://www.usb.org.