xvalue

An lvalue (so-called, historically, because lvalues could appear 
on the left-hand side of an assignment expression) designates a
function or an object. [Example: If E is an expression of pointer
type, then *E is an lvalue expression referring to the object or
function to which E points. As another example, the result of calling
a function whose return type is an lvalue reference is an lvalue

An xvalue (an “eXpiring” value) also refers to an object, usually 
near the end of its lifetime (so that its resources may be moved,
for example). An xvalue is the result of certain kinds of expressions
involving rvalue references. [Example: The result of calling a 
function whose return type is an rvalue reference is an xvalue.]

A glvalue (“generalized” lvalue) is an lvalue or an xvalue.

An rvalue (so-called, historically, because rvalues could appear
on the right-hand side of an assignment expression) is an xvalue,
a temporary object or subobject thereof, or a value that is not
associated with an object

A prvalue (“pure” rvalue) is an rvalue that is not an xvalue.
[Example: The result of calling a function whose return type
is not a reference is a prvalue]