The word esoteric generally relates to that which is known and accepted by a restricted number of people (contrast exoteric). The word esotericism (or esoterism) used in a general sense can simply mean any knowledge which is secret or confidential. Used in its more specific sense it refers to the knowledge of those who claim to have had supernatural experiences. While these experiences typically are not validated by scientific experiments, scientific proof is not always necessary for belief. Esoteric experiences tend to be highly subjective and so are difficult to study with the scientific method. There exists some skepticism about these experiences due to this lack of empirical evidence and sufficient proof; however, among supporters of esotericism, most believe that measurement of this phenomena simply exceeds current scientific capabilities. Esotericism is one of the subjects studied under the discipline parapsychology.