diff --git a/staging/src/k8s.io/client-go/tools/cache/index.go b/staging/src/k8s.io/client-go/tools/cache/index.go
index 15acb168ef2..2a4bcbc47d6 100644
--- a/staging/src/k8s.io/client-go/tools/cache/index.go
+++ b/staging/src/k8s.io/client-go/tools/cache/index.go
@@ -23,17 +23,27 @@ import (
 	"k8s.io/apimachinery/pkg/util/sets"
 )
 
-// Indexer is a storage interface that lets you list objects using multiple indexing functions
+// Indexer is a storage interface that lets you list objects using multiple indexing functions.
+// There are three kinds of strings here.
+// One is a storage key, as defined in the Store interface.
+// Another kind is a name of an index.
+// The third kind of string is an "indexed value", which is produced by an
+// IndexFunc and can be a field value or any other string computed from the object.
 type Indexer interface {
 	Store
-	// Retrieve list of objects that match on the named indexing function
+	// Index returns the stored objects whose set of indexed values
+	// intersects the set of indexed values of the given object, for
+	// the named index
 	Index(indexName string, obj interface{}) ([]interface{}, error)
-	// IndexKeys returns the set of keys that match on the named indexing function.
-	IndexKeys(indexName, indexKey string) ([]string, error)
-	// ListIndexFuncValues returns the list of generated values of an Index func
+	// IndexKeys returns the storage keys of the stored objects whose
+	// set of indexed values for the named index includes the given
+	// indexed value
+	IndexKeys(indexName, indexedValue string) ([]string, error)
+	// ListIndexFuncValues returns all the indexed values of the given index
 	ListIndexFuncValues(indexName string) []string
-	// ByIndex lists object that match on the named indexing function with the exact key
-	ByIndex(indexName, indexKey string) ([]interface{}, error)
+	// ByIndex returns the stored objects whose set of indexed values
+	// for the named index includes the given indexed value
+	ByIndex(indexName, indexedValue string) ([]interface{}, error)
 	// GetIndexer return the indexers
 	GetIndexers() Indexers
 
@@ -42,7 +52,7 @@ type Indexer interface {
 	AddIndexers(newIndexers Indexers) error
 }
 
-// IndexFunc knows how to provide an indexed value for an object.
+// IndexFunc knows how to compute the set of indexed values for an object.
 type IndexFunc func(obj interface{}) ([]string, error)
 
 // IndexFuncToKeyFuncAdapter adapts an indexFunc to a keyFunc.  This is only useful if your index function returns