A standard is "a recognized unit of comparison by which the correctness of others can be determined." Another definition is "a set of characteristics or qualities that describes features of a product, process, or service." (ANSI Course "Why Standards Matter")
Who produces them?
Scientific and Professional Organizations such as the ASTM, ASME, IEEE, trade organizations, and governments create and produce standards. Standards are produced nationally and internationally. In the United States, the American National Standards Institute (ANSI) coordinates many standards producing organizations. ANSI is also the sole US representative to the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC).
Health Level 7 (HL7) is an ANSI accredited standards development organization that produces documentation that describes how clinical information will be exchanged between disparate healthcare applications.
IEEEXplore contains the full text of IEEE standards including many related to health informatics.
How do I identify which ones I need?
There are many search tools on the internet to assist you in locating standards in your area of study. Some of these are listed on the page "Finding Standards"