From Longman Business Dictionary
de factode fac·to /ˌdeɪ ˈfæktəʊ dɪ ˈfæktoʊ, ˌdeɪ-/ adjectiveadj, adverbadv formalLAW really existing, even if there is no formal legal document etc to prove itPrior to the Companies Act 1976, resignation would have constituted a de facto breach of contract.