Standards are officially sanctioned guidelines for design.
The default behaviour or officially approved guidelines for design or technology.
Standards differ from conventions in that standards can be defined and enforced by an institution or party whereas conventions are more based on mass acceptance. (I.e. it is convention to make links for mobile devices clickable size, but it is according to company XYZ's standard to make them at least 48px x 48px in size.)
Also see human-interface-guidelines for questions containing documented guidelines about how an interface should be look, feel and work.