The World Wide Web Consortium (w3c)
In very general terms, Wikipedia defines "best practice" as: "a method or technique that has consistently shown results superior to those achieved with other means, and that is used as a benchmark." Best practices are known throughout many fields, such as healthcare, public policy, and engineering. In private business best practices govern all sorts of both business and operational strategies required so that organizations may conduct trade together and to insure consumer protection at all levels.
Often, best practices are not as strictly enforced as "standards", which are more formal statements about requirements. For example, most guidelines governing food safety are expressed as standards, which are enforced with the law. The intent of a "best practice" is often more to enhance the consumer product or experience rather than preventing harm to the consumer. In cases where harm may be done to the consumer, rules are expressed as standards.
In order to define broad standards, there must be larger organizations that can bring individuals and individual companies together to agree on a common platform. This can be addressed through different kinds of organizations, but the one that actually publishes the HTML, CSS and many other specifications is the World Wide Web Consortium (W3C). The W3C publishes both best practices and Web Standards, such as HTTP, CSS, Accessibility and more.
For web development, the W3C is the ultimate authority on how web technologies are implemented. This has become the case after many years of effort on the part of several leaders in the community and, ultimately, with the cooperation of major businesses such as Google, Microsoft, Adobe, Mozilla and many more. The Web Standards Project (WaSP) was the major effort that led to the adoption of common standards for operation across different web browsers and web authoring tools. Today, it is recognized that new clients must all work in compliance with the W3C standards. This has allowed web browsers to proliferate. Now, we can browse the web on televisions, mobile devices, game systems, and much more, all supported by a common set of operating standards.