@@ -180,6 +180,9 @@ The command
 In this example, we use it to find Maja's telephone number.
 .SS Pathnames and the current directory
 Files live in a large tree, called the file hierarchy.
+In this hierarchy, there are many
+.IR directories ;
+a directory is simply a file that can hold other files as opposed to text.
 Each file has a
 .I "pathname"
 describing the location of the file from the root of the tree