This is sometimes called a reverse link. It defines the relationship between a document and another that calls it. The linkage is defined from the destination document's viewpoint.
This property supports the same HTML version 4.0 standard link types as the rel property. Refer to that topic for details.
When used or tested within a script, any comparisons should be case-insensitive.
As rel and rev properties are complementary, the values in them are likely to be related. For example, if one contains the value "next" then the other is likely to contain "previous".