Clarify the meaning of normal and subnormal.

Doc/library/decimal.rst

@@ -548,8 +548,11 @@ Decimal objects
 
    .. method:: is_normal()
 
-      Return :const:`True` if the argument is a *normal* finite number.  Return
-      :const:`False` if the argument is zero, subnormal, infinite or a NaN.
+      Return :const:`True` if the argument is a *normal* finite non-zero
+      number with an adjusted exponent greater than or equal to *Emin*.
+      Return :const:`False` if the argument is zero, subnormal, infinite or a
+      NaN.  Note, the term *normal* is used here in a different sense with
+      the :meth:`normalize` method which is used to create canonical values.
 
       .. versionadded:: 2.6
 
@@ -577,7 +580,8 @@ Decimal objects
    .. method:: is_subnormal()
 
       Return :const:`True` if the argument is subnormal, and :const:`False`
-      otherwise.
+      otherwise. A number is subnormal is if it is nonzero, finite, and has an
+      adjusted exponent less than *Emin*.
 
       .. versionadded:: 2.6