Composite supply means a supply is comprising two or more goods/services, which are naturally bundled and supplied in with each other in the ordinary course of business where one of which is a principal supply.

In other words, composite supply is a supply of two or more goods or services that are only sold as a set and cannot be sold individually.

Suppose you purchase some goods from a supplier. The supplier sends you the goods along with insurance, fright and installation cost, all shown separately in the tax invoice. Here, we can identify the goods as principal supply and the insurance, fright and installation cost are composite supplies because the insurance, fright and installation cost can not be sold individually. Without the principal supply, they have no meaning.