That's a somewhat confusing defintion of lvalue. A lvalue, quite literally, is something that can appear on the left hand side of an = operator -- that is, something that can be assigned to. In perl, that includes assignable variables (read: almost all variables), and calls to lvalue subroutines (including lvaluable builtins like substr, and user-defined subroutines with the :lvalue attribute). (The first half of that includes, of course, any expression that results in an assignable variable, such as $foo->{bar}{baz}{quux}[-1].) The 42 in 42=1; is a non-lvalue in a slot that needs an lvalue. Note that there are places that need an lvalue other then the right-hand-side of a = operator, such as all the *= operators, ++ and --, and some sub arguments, sometimes only in some situations. In general, if an operation is going to modify something, that something must be an lvalue -- which is another defintion of lvalue: "something that can be modified".