Study of existence
Explanation: It's something that is a part of philosophy, in other words putting things into categories with the theories that explain the ideology or nature of existence by describing it or its parts in substance or causes. Types: object, kind, mode, and attributes
Simple example
trying to explain or rather "prove" god exists based on causes like say you made a wish once and it came true or maybe how your life has been better because you have beliefs, etc.