What is "HID Keyboard Device" in Device Manager (Win 7)

A HID Keyboard Device is just a generic keyboard. Keyboard devices are now common enough that basic drivers and support for them are a solved problem. Odds are one of the devices listed in your device manager represents the keyboard used to type your question.

But what about the other one? It turns out that lots of things are, at their core, "keyboards". Barcode scanners, for example, are often built to look like a simple keyboard from the perspective of the computer. So are some infrared devices, joysticks/gamepads, smart card readers, and even fingerprint sensors. But, I suspect in your case, the 2nd device is what processes the signals when you use your Fn or Fn Lock key.

HID is a TLA (Three Letter Acronym) for "Human Interface Device". Microsoft uses this term for most input devices (keyboard and mice typically). In the device manager, it just refers to keyboard that uses the standard microsoft driver. You may have two if you have used a docking port or have installed other speciality keyboard drivers.