What is the best definition of "esoteric"?

The best definition of "esoteric" is "known only by a select few." This term typically refers to knowledge or information that is obscure, specialized, and not widely understood or available to the general population. Esoteric subjects often require a certain level of expertise or a particular background to fully comprehend, making them exclusive to those who have the necessary insight or training. This idea contrasts sharply with definitions that suggest the information is commonly known or easily accessible, as those options imply a level of familiarity and understanding that does not align with the essence of what is considered esoteric.