Replying to [balu1234]:
An Answer by Nano1 is the correct understanding of what a combined B/L is.
It is carriage of goods by at least two different modes of transport, from a place at which the goods are taken in charge to a place designated for delivery.
It can be a combination of road, rail, inland waterway, sea or air. In this respect, only one BL is issued to cover the whole journey which is called 'Combined Bill of Lading'.
Other explanations are just a shot in the dark. Nice to read though.