  Driven by the vision of intelligent connection of everything and digital twin
towards 6G, a myriad of new applications, such as immersive extended reality,
autonomous driving, holographic communications, intelligent industrial
internet, will emerge in the near future, holding the promise to revolutionize
the way we live and work. These trends inspire a novel technical design
principle that seamlessly integrates two originally decoupled functionalities,
i.e., wireless communication and sensing, into one system in a symbiotic way,
which is dubbed symbiotic sensing and communications (SSaC), to endow the
wireless network with the capability to "see" and "talk" to the physical world
simultaneously. Noting that the term SSaC is used instead of ISAC (integrated
sensing and communications) because the word ``symbiotic/symbiosis" is more
inclusive and can better accommodate different integration levels and evolution
stages of sensing and communications. Aligned with this understanding, this
article makes the first attempts to clarify the concept of SSaC, illustrate its
vision, envision the three-stage evolution roadmap, namely neutralism,
commensalism, and mutualism of SaC. Then, three categories of applications of
SSaC are introduced, followed by detailed description of typical use cases in
each category. Finally, we summarize the major performance metrics and key
enabling technologies for SSaC.
