Sexual objectification, in the broadest terms, involves (at least) treating people as things. Philosophers have offered different accounts of what, more precisely, this involves. According to the conjoint view of Catherine Mackinnon and Sally Haslanger, sexual objectification is necessarily morally objectionable. According to Martha Nussbaum, it is not: there can be benign instances of it, in the course of a healthy sexual relationship, for instance. This is taken to be a serious disagreement, both by Nussbaum and by recent commentators such as Lina Papadaki. However it isn't a serious disagreement, for the two theories have different aims and methodology, and are not rivals. They both could be apt, simultaneously.
Sussex Research Online (http://sro.sussex.ac.uk/56971/3/Sexual_objectification_AnalysisStock.pdf)