A Standard is a set of guidelines for consistent performance or outcomes for goods, services or processes (products). It is established by a recognised organisation who, via consensus, sets criteria and details in a formal document.
The official definition of a standard from ISO/IEC Guide 2:1996, Standardisation and related activities - General vocabulary is:
"A standard is a document established by consensus and approved by a recognised body that provides, for common and repeated use, rules, guidelines or characteristics for activities or their results, aimed at the achievement of the optimum degree of order in a given context. Note: standard should be based on the consolidated results of science, technology and experience, and aimed at the promotion of optimum community benefits."