Believe it or not, in certain contexts, this is an appropriate use of dimension. Dimensions can be thought of as parameters, essentially. In 3d space, you have 3 parameters, length, width, and height. Add in time and you have 4d spacetime. From there, if you’re defining a system with more parameters, it’s a higher dimensional space. A movie with 3 spatial dimensions, then programmed smell releases, like someone else mentioned, would then be 4 dimensions: l,w,h,s. The reality is, it’s a bit silly and definitely a marketing gimmick to refer to your movie experience as “9d”, but it’s not entirely incorrect.