1580s, "the whole world, cosmos," from Old French univers (12c.), from Latin universum "the universe," noun use of neuter of adj. universus "all together," literally "turned into one," from unus "one" (see one) + versus, past participle of vertere "to turn" (see versus). Properly a loan-translation of Greek to holon "the universe," noun use of neuter of adj. holos "whole" (see safe (adj.)).
In ontology, the set of all entities that can be represented in some declarative language or other formal system.
Each entity is represented by a name and may have some human-readable description of its meaning. Formal axioms constrain the interpretation and well-formed use of these names.