What is iPhone Firmware
By What is iPhone Firmware?
It basically software which is running on your iPhone and other Apple devices.
The iPhone OS, known as OS X iPhone in its early history, is the operating system developed by Apple Inc. for the iPhone and iPod touch. Like Mac OS X, from which it was derived, it uses the Darwin foundation. iPhone OS has four abstraction layers: the Core OS layer, the Core Services layer, the Media layer, and the Cocoa Touch layer. The operating system takes less than 240 Megabytes of the device’s total memory storage.
quoted from Wikipedia
How-to check iPhone firmware?
See: How-to Check iPhone Firmware Version
iPhone Firmware 
