Embedded system: a system dedicated to a specific purpose and consisting of a compact, fast and extremely reliable operating system that controls the microprocessor located inside a device.
An embedded system typically must operate within specified time constraints. When such constraints exist, we call the embedded system a real-time system. This means that the system must respond to inputs or events within prescribed time limits, and the system as a whole must operate within specified time constraints. Thus, a real-time system must not only produce correct results, but also it must produce them in a timely fashion. The timing of the results is sometimes as important as their correctness.