Nesting is the placement of similar structures within each other, like the Matrushka dolls, with a larger structure containing a smaller structure, and so on.
In arithmetic, we often see nested parentheses.
((3 - 4) * sin(30) + 16) / (15 - (3 / 4))
Computer languages also use nested, both in arithmetic and in control structures. In PHP, nesting is infinite.[1]