During the last decade, Cognitive Radio (CR) has become a popular research topic. The availability of radio spectrum is in shortage, and CR technology can solve the problem by enabling dynamic spectrum access. This innovative technology has been used to manage the radio spectrum since it was introduced. These developments have led to rapid advances in this research field. A review of recent advances in Spectrum Sensing (SS) is presented in this paper, from its origins to its present state. A CR network has been found to be a highly effective and intelligent technology. Frequency spectrum is a bounded natural resource and an essential component of wireless communication networks. We explored CR in this paper and its various phases. Different definitions of CR are then presented from various institutions. Many different types of communications systems use CR techniques. It is anticipated that they will improve commercial and military data services, as well as increase the use of underutilized radio frequencies. In this paper, CR standards have been discussed, as well as its applications in various areas.