Adds «value» refs #728

doc/Language/glossary.pod6

@@ -1122,6 +1122,8 @@ A L<type object|https://docs.perl6.org/language/classtut#index-entry-type_object
 =head1 value
 X<|value>
 
+A value is what is actually contained in a container such as a variable. Used in expresions such as L<lvalue>, to indicate that that particular container can be assigned to.
+
 =head1 Value type
 X<|Value type>