To fully appreciate the good example projects using embedded Linux mentioned here, it is important that you understand the details about what embedded software is today. The easiest way to describe embedded software is to say that embedded software is the software which is supplied with electronic hardware like consumer electronics or a component such as a computer graphics card. We can also describe embedded software as the software which is programmed directly onto the hardware components.
These descriptions would therefore classify the lesser thought of device drivers as being embedded software even though they reside in larger operating systems.
A Better Understanding
The above descriptions however, may or may not be enough to get a clear picture of embedded software.