-#include <signal.h> /* signal functions */
-#include <errno.h> /* error code */
-#include <string.h> /* error strings */
-#include <stdlib.h>
+#include <signal.h> /* signal constants, types and functions */
+#include <errno.h> /* error definitions and routines */
+#include <string.h> /* C strings library */
+#include <stdlib.h> /* C standard library */