"Subjective" refers to a chunk of the world that is an opinion. When I say, for instance, that the Eiffel Tower is humongous in reference to its size, that's opinion. It's what I think about the thing.
"Objective" refers to a chunk of the world that is descriptive. When I describe I try to be accurate, so I may draw on facts or appropriate metaphor to get my point across. I'm conveying a description of the chunk, and what I convey is going to be as I understand it to be, with the intent that you understand it as I do.
"Relative" refers to a chunk in relation to something, usually a measure of some sort. The Eiffel Tower is relatively large, and that's a fact. It's implied that it's being compared to other towers and structures, which are then its measure.