Big data is an emerging research area where common terminology is still evolving. Different perspectives to the research area and terminology exist, but a common definition for big data does not exist. We have performed a systematic mapping study in order to identify different big data definitions and their perspectives. As a result, we present a state-of-the-art review of the current status in big data definitions, discuss the shortcomings of the current definitions, and propose possible solutions for the shortcomings. The paper contributes to the emerging big data research by analyzing current definitions of big data from different perspectives, suggesting enhancement to the terminology as well as pointing out new research avenues. In addition, the article helps new researchers and practitioners to understand what big data is, and bridges the knowledge between theory and practice.