Esoteric

That which is esoteric is meant to be understood by a few who have a specialized knowledge of a topic.  For example, the statement “The difference between the hypostatic union and the communicatio idiomatum is, in part, the difference between nature and properties.”  In other words, the statement requires specialized training in advanced theological concepts in order to be understood.  Therefore, relatively few people understand the statement.  It is therefore, esoteric.