Index: wp-admin/includes/class-wp-ms-users-list-table.php
===================================================================
--- wp-admin/includes/class-wp-ms-users-list-table.php	(revision 16421)
+++ wp-admin/includes/class-wp-ms-users-list-table.php	(working copy)
@@ -117,7 +117,7 @@
 	function get_columns() {
 		$users_columns = array(
 			'cb'         => '<input type="checkbox" />',
-			'login'      => __( 'Login' ),
+			'login'      => __( 'Username' ),
 			'name'       => __( 'Name' ),
 			'email'      => __( 'E-mail' ),
 			'registered' => _x( 'Registered', 'user' ),
Index: wp-admin/includes/class-wp-users-list-table.php
===================================================================
--- wp-admin/includes/class-wp-users-list-table.php	(revision 16421)
+++ wp-admin/includes/class-wp-users-list-table.php	(working copy)
@@ -120,7 +120,7 @@
 	function get_columns() {
 		return array(
 			'cb'       => '<input type="checkbox" />',
-			'username' => __( 'Login' ),
+			'username' => __( 'Username' ),
 			'name'     => __( 'Name' ),
 			'email'    => __( 'E-mail' ),
 			'role'     => __( 'Role' ),