Issues of energy crisis and global warming push implementation of energy efficiency policies and programs as important mitigation efforts, particularly at consumer level. Load monitoring (LM) serves to furnish real-time feedback consumption information for the measures of efficient energy management strategies. Conventional LM is intrusive (ILM) which is costly and time-consuming in hardware installation. Nonintrusive load monitoring (NILM) option, on the other side, is relatively cheaper, ease of installation, and good scalability in commercialization values. The demand control of this approach has the potential of 20% energy-saving. In this paper, we discuss the fundamental stages of typical NILM framework and giving a taxonomy of appliance models with device signatures. We highlight main use-cases and formulate the challenges of future research directions, particularly the use of cloud computing and smart meters in NILM to unlock new seamless services for smart home and smart grid sectors.