A metadata standard or schema is a set group of elements that have been standardized for a particular field. Some scientific disciplines already have established metadata standards for data sets. Additionally, some data repositories also have their own standards. One of the standards listed below might be exactly what you need to document your data. If there is not a standard already in place for your data, there are several general purpose schemas that you can adapt to your needs. Your liaison librarian will be familiar with the metadata standards used in your discipline.
General: Dublin Core | MODS
Social Science: DDI
Humanities: TEI | VRA
Sciences: Darwin Core | ITIS | EML | DIF | SEED | FGDC | ISO 19115 | GIF
Access to Biological Collection Data (ABCD)
Virtual Astronomy Multimedia Project (VAMP)
Electronic Metastructure for Endangered Languages Data (E-MELD)
And visit Andrei Lopatenko's Resource Guide to Metadata for Science, Research, Education, and Technology for additional very specific metadata schemas.