Your perception is what it is, and the fact that you see it as you see it is definitively true and certain. The nature of the object seen is a matter we are not equipped to address, as per our wholly subjective nature.
For this reason, I define objectivity by consistency and consensus of subjective experience. A dream you have is not subject to consensus, since no one else has the experience of it, so it is not deemed “objective” and we may therefore call it “subjective” by way of practical distinction.
But really, subjective experience is all we ever have to go on, as even consensus is perceived by each participant subjectively, and there’s no way of knowing if the other people (and their reports) exist outside your own perception.