Cyc® (pronounced like psych) is the name of an artificial intelligence project started in 1984 by Doug Lenat. The name is now a registered trademark owned by Cycorp in Austin, Texas; however, there is also an OpenCyc project that is available as open source.
The original goal of the project was ambitious – encode all human knowledge in a format that a machine could process and use for reasoning (see artificial intelligence).
So far over a million human-defined assertions, rules or common sense ideas called ontologies make up the Cyc knowledge base. Similar to Roget's original thesaurus, an ontology is designed to capture a large portion of everyday human knowledge about the world. For example, a Cyc system might have a nature ontology which "knows" that clouds are usually in the sky. A temporal ontology might know that over time puppies become adult dogs, while a gravity ontology could tell it that objects fall towards the ground if not supported.