An Embedded System is a small, specialized, computer operating inside a device that is not primarily a computer. It typically consists of a Microcontroller and in some cases external memories such as RAM and/or Flash memory.
Anything in today's world that has a display, or keys, or controls a motor, has an embedded computer which is considered an Embedded System. Examples range from telephones and cameras, to modern coffee makers and washing machines, to trains, planes, and automobiles, up to satellites and lunar rovers.
While new hardware and software is constantly entering the market, and being replaced over time, it is impossible to imagine any version of our future world in which Embedded Systems to do not play a major role.