I imagine it could most likely mean one of two things. It makes me think first of depth of flavors, as in how many flavor profiles are present. Think of something like Indian or Thai food that usually incorporates several distinct flavors vs. something like mac&cheese. Second, it could mean the depth of a singular flavor. You may have had an apple that tasted amazing because it was so much more apple-y than any you'd had before. One of the reasons salt is so prevalent in cooking as it brings out the sui generis quality of a lot of ingredients.