diff --git a/pep-0418.txt b/pep-0418.txt
index a8a852077..3c7fed5ec 100644
--- a/pep-0418.txt
+++ b/pep-0418.txt
@@ -219,6 +219,27 @@ Return a dictionary with the following keys:
      daemon)
 
 
+Definitions
+===========
+
+Monotonic
+---------
+
+A monotonic clock cannot go backward. It may give the same value for two close
+reads depending on the clock resolution.
+
+On Linux, CLOCK_MONOTONIC is a monotonic clock but its rate is adjusted by NTP.
+
+Steady
+------
+
+A steady clock is a clock with a stable rate.
+
+The C++ Timeout Specifiction uses the following definition: "Objects of class
+steady_clock represent clocks for which values of time_point advance at a
+steady rate relative to real time. That is, the clock may not be adjusted."
+
+
 Hardware clocks
 ===============