An open standard is a standard that is openly accessible and usable by anyone. It is also a prerequisite to use open license, non-discrimination and extensibility. Typically, anybody can participate in the development. There is no single definition, and interpretations vary with usage.

The terms open and standard have a wide range of meanings associated with their usage. There are a number of definitions of open standards which emphasize different aspects of openness, including the openness of the resulting specification, the openness of the drafting process, and the ownership of rights in the standard. The term "standard" is sometimes restricted to technologies approved by formalized committees that are open to participation by all interested parties and operate on a consensus basis.

The definitions of the term open standard used by academics, the European Union, and some of its member governments or parliaments such as Denmark, France, and Spain preclude open standards requiring fees for use, as do the New Zealand, South African and the Venezuelan governments. On the standard organisation side, the World Wide Web Consortium (W3C) ensures that its specifications can be implemented on a royalty-free basis.

Many definitions of the term standard permit patent holders to impose "reasonable and non-discriminatory licensing" royalty fees and other licensing terms on implementers or users of the standard. For example, the rules for standards published by the major internationally recognized standards bodies such as the Internet Engineering Task Force (IETF), International Organization for Standardization (ISO), International Electrotechnical Commission (IEC), and ITU-T permit their standards to contain specifications whose implementation will require payment of patent licensing fees. Among these organizations, only the IETF and ITU-T explicitly refer to their standards as "open standards", while the others refer only to producing "standards". The IETF and ITU-T use definitions of "open standard" that allow "reasonable and non-discriminatory" patent licensing fee requirements.

There are those in the open-source software community who hold that an "open standard" is only open if it can be freely adopted, implemented and extended. While open standards or architectures are considered non-proprietary in the sense that the standard is either unowned or owned by a collective body, it can still be publicly shared and not tightly guarded. The typical example of “open source” that has become a standard is the personal computer originated by IBM and now referred to as Wintel, the combination of the Microsoft operating system and Intel microprocessor. There are three others that are most widely accepted as “open” which include the GSM phones (adopted as a government standard), Open Group which promotes UNIX and the like, and the Internet Engineering Task Force (IETF) which created the first standards of SMTP and TCP/IP. Buyers tend to prefer open standards which they believe offer them cheaper products and more choice for access due to network effects and increased competition between vendors.

Open standards which specify formats are sometimes referred to as open formats.

Many specifications that are sometimes referred to as standards are proprietary and only available under restrictive contract terms (if they can be obtained at all) from the organization that owns the copyright on the specification. As such these specifications are not considered to be fully open. Joel West has argued that "open" standards are not black and white but have many different levels of "openness". A more open standard tends to occur when the knowledge of the technology becomes dispersed enough that competition is increased and others are able to start copying the technology as they implement it. This occurred with the Wintel architecture as others were able to start imitating the software. Less open standards exist when a particular firm has much power (not ownership) over the standard, which can occur when a firm's platform “wins” in standard setting or the market makes one platform most popular.