Metadata is often defined as "data about data". It is also known as data documentation. Metadata is used to describe and document research data. Metadata facilitates searching for data in an archive or repository and makes the data easily understood by anyone who wants to use the data. It describes the who, what, when, where, how and why about data.
There are two types of metadata
Structural metadata: indicates how compound objects are put together. For example, how pages are ordered to form chapters.
Descriptive metadata: describes a resource for purposes such as discovery and identification. It can include elements such as title, abstract, author, and keywords.
A number of elements should be included in metadata. Some of these are listed here.
Metadata standards are uniform ways to descrbe data. Some disciplines have devised metadata standards and others have not. Common metadata standards are Dublin Core and the Data Documentation Initiative (DDI) ( see links below). Here are some sources to find metadata standards.