diff --git a/Doc/library/math.rst b/Doc/library/math.rst
@@ -84,7 +84,8 @@ Number-theoretic and representation functions
 
 .. function:: fmod(x, y)
 
-   Return ``fmod(x, y)``, as defined by the platform C library. Note that the
+   Return the floating-point remainder of ``x / y``,
+   as defined by the platform C library function ``fmod(x, y)``. Note that the
    Python expression ``x % y`` may not return the same result.  The intent of the C
    standard is that ``fmod(x, y)`` be exactly (mathematically; to infinite
    precision) equal to ``x - n*y`` for some integer *n* such that the result has