Standards, specifications, and codes are generally used in the engineering design process.
-A standard is an approved set of criteria that define the performance, design, or the process of constructing a product; tells you how to do something. It is usually represented by the acronym of the issuing organization followed by a number and the date of issuance - examples:
-Codes are organized collections of mandatory standards that have been made into law by a governmental authority. They tell you what you need to do.
-A specification is a set of conditions and/or requirement used mostly for procurement and manufacturing purposes; they may be referenced or included in standards. They outline the requirements of a specific product or company.
Who produces standards?
Scientific and professional organizations (such as ASME, IEEE, etc), trade organizations, and governments create standards, both nationally as well as internationally. In the United States, the American National Standards Institute (ANSI) coordinates many standards producing organizations.
Resources:
SMU Research Guide on Engineering Standards