  The increasing bandwidth requirement of new wireless applications has lead to
standardization of the millimeter wave spectrum for high-speed wireless
communication. The millimeter wave spectrum is part of 5G and covers
frequencies between 30 and 300 GHz corresponding to wavelengths ranging from 10
to 1 mm. Although millimeter wave is often considered as a communication
medium, it has also proved to be an excellent 'sensor', thanks to its narrow
beams, operation across a wide bandwidth, and interaction with atmospheric
constituents. In this paper, which is to the best of our knowledge the first
review that completely covers millimeter wave sensing application pipelines, we
provide a comprehensive overview and analysis of different basic application
pipeline building blocks, including hardware, algorithms, analytical models,
and model evaluation techniques. The review also provides a taxonomy that
highlights different millimeter wave sensing application domains. By performing
a thorough analysis, complying with the systematic literature review
methodology and reviewing 165 papers, we not only extend previous
investigations focused only on communication aspects of the millimeter wave
technology and using millimeter wave technology for active imaging, but also
highlight scientific and technological challenges and trends, and provide a
future perspective for applications of millimeter wave as a sensing technology.
