Any variable defined in your program has two values, the "lvalue" and the "rvalue".
lvalue is the left value, and rvalue is the right value.
suppose you have defined a variable of int type:
x = 10;
in above line, you say that, save the value 10 (rvalue) in the memory location of x (lvalue).
see this example and note the difference:
int x, y;
first you defined two variables of type int, then in line two you say:
save the value `10` in the memory location of variable `x`, and in the third line you say: save the value in memory location `x`, into the memory location of variable `y`.
So, `x` on the left -lvalue- (at line 2) are refereed as `the address of x`, but x on the right -rvalue- (at line 3) are refereed as `the value at the address of x`.