De facto is a Latin expression that means "in fact" or "in practice" but not spelled out by law. It is commonly used in contrast to de jure (which means "by law") when referring to matters of law, governance, or technique (such as standards), that are found in the common experience as created or developed without or contrary to a regulati ...on. When discussing a legal situation, de jure designates what the law says, while de facto designates action of what happens in practice.

A de facto standard is a standard (formal or informal) that has achieved a dominant position, as a tradition, or by enforcement, or market dominance. It has not necessarily received formal approval by way of a standardization process, and may not be an official standard document.

In social sciences, it is a usual solution for a coordination problem. De facto standard is the better choice into situations in which all parties can realize mutual gains only by making mutually consistent decisions.