Sawdee - loosely defined, embedded systems are essentially computers in places where a computer is used, but not in the way that a desktop machine is used.
Often they are used for monitoring, POS systems, that sort of thing. Washing machines are possibly a slightly off-the-wall idea, but a processor used in a washing machine to control temperatures, spin cycles and the UI between the operator and the device would class as an embedded system. Clearly there are LOTS of embedded devices in medicine, as we use a lot of monitoring equipment. You don't know that there's a PC there, but it's there, and it's doing lots of maths for you behind your back.
RISC OS makes a nice embedded machine because it's fast, efficient, has rock solid stability and you can use low power consumption chips which don't need crazy cooling. Unlike desktop machines, factors like lack of a web browser aren't really issues.