Embedded system is an important and popular application system for information technology. The applications of embedded system are depended on embedded hardware and software. In fact, applications of embedded systems have changed life of people in the world. They can be found anywhere, and almost can be used in every field. Since there are multiple definitions for the terminology, few people exactly know the concept of an embedded system. In this paper, some important concepts and definitions of embedded system are discussed and analyzed. The research is helpful to understand the embedded systems and apply them better.