1.nounA legally undeclared spouse; a partner in a spousal relationship which is not officially declared as a marriage, comparable to a common law husband or wife.
2.adjectiveIn fact or in practice; in actual use or existence, regardless of official or legal status. (Often opposed to de jure.)
"Although the United States currently has no official language, it is largely monolingual with English being the de facto national language."
3.adverb(modal) In practice; in actual use or existence, regardless of official or legal status.