There is a wide consensus by the research community and the industry that it will not be possible to satisfy future mobile traffic demand and application requirements by simply evolving the current fourth-generation architecture. Instead, there is a need for a considerable revision of the mobile network system: such an effort is commonly referred to as the future fifth-generation (5G) architecture, and large-scale initiatives all around the globe have been launched worldwide to address this challenge. While these initiatives have not yet defined the future 5G architecture, the research community has already invested a very substantial effort on the definition of new individual technologies. The fact that all new proposals are tagged as 5G has created a lot of confusion on what 5G really is. The aim of this article is to shed some light on the current status of the 5G architecture definition and the trends on the required technologies. Our key contributions are the following: (1) we review the requirements for 5G identified by the different worldwide initiatives, highlighting similarities and differences; (2) we discuss current trends in technologies, showing that there is a wide consensus on the key enablers for 5G; and (3) we make an effort to understand the new concepts that need to be devised, building on the enablers, to satisfy the desired requirements.