Standards are commonly agreed upon references like controlled vocabularies, scales, Common Data Elements (CDEs), data formats, and definitions. An example of a terminology standard is ICD-10, the International Classification of Diseases. There are also data exchange standards, like DICOM.
NIH is requiring the use of standards to increase interoperability, enabling data sets to "'use and speak the same language' via [the] use of standardized vocabularies" (NIH, 2018, p. 6). Sharing data with appropriate standards reduces the time needed to clean and prepare the data for reuse, furthering scientific discovery.
As part of your DMS plan, you need to indicate what standards you will apply to the scientific data and metadata you share OR indicate that no consensus standards exist.
Your NIH ICO may also require or recommend the use of certain standards, which should be stated in this section of your DMS plan.
Repositories may also require particular standards. That information can usually be found on the repository website or by searching for the repository on FAIRsharing and looking at the "related standards" section (e.g. NAHDP).