1. (philosophy) relating to physical or real existence, as opposed to theoretical or conceptual nature
   "ontological speculations";
   - ontic
    
2. (philosophy) relating to the nature and study of being or existence in general
   "The ontological argument attempts to prove God's existence from the concept of a perfect being"
    
3. (computing) describing a formal system that defines categories, properties, and relations between concepts, data, or entities
   "The team developed an ontological framework for their knowledge base"

Encyclopedia: Ontological