diff --git a/doc/api/util.md b/doc/api/util.md
index 6a6eaf65e7ef50..469bcf2b6455e9 100644
--- a/doc/api/util.md
+++ b/doc/api/util.md
@@ -1392,6 +1392,11 @@ added: v10.0.0
 * Returns: {boolean}
 
 Returns `true` if the value is a native `External` value.
+A native `External` value is a special type of object whose
+data is not stored within the JavaScript managed heap
+and does not conform to standard JavaScript types. Such
+objects are created either by Node.js internals or native
+addons and are wrapped by a JavaScript object.
 
 ### `util.types.isFloat32Array(value)`
 <!-- YAML