Historically, lvalues and rvalues were so-called
because they could appear on the left- and right-hand side of an assignment
(although this is no longer generally true);
glvalues are “generalized” lvalues,
prvalues are “pure” rvalues,
and xvalues are “eXpiring” lvalues.
Despite their names, these terms classify expressions, not values.
— end note