diff -u b/core/modules/rdf/rdf.api.php b/core/modules/rdf/rdf.api.php
--- b/core/modules/rdf/rdf.api.php
+++ b/core/modules/rdf/rdf.api.php
@@ -16,7 +16,7 @@
  * Many common namespace prefixes are defined in rdf_rdf_namespaces(). However,
  * if a module implements rdf mappings that use prefixes that are not
  * defined in rdf_rdf_namespaces(), this hook should be used to define the new
- * namespace prefix.
+ * namespace prefixes.
  *
  * @return
  *   An associative array of namespaces where the key is the namespace prefix