"Ketosis" isn't a place, although some might say it's almost a state of mind. In very simple terms, ketosis is when the body utilizes ketone bodies (fat) for fuel rather than glucose (sugar). Our bodies can use either fuel for energy and keeping the lights on but in general can use one or the other. (It's not 100% for either but rather the body will burn either glucose or fat for the vast majority of its needs at any given time)