A free transfer is a term used in public transportation, it refers to allowing a rider to switch from one vehicle to another without paying an additional fare

Fare

A fare is the fee paid by a passenger allowing him or her to make use of a public transport system: rail, bus, taxi, etc. In the case of air transport, the term airfare is often used.-Uses:...

. This can be done by having both vehicles stop within the same fare control area, by issuing the rider a special ticket (also called a "free transfer") or by using an electronic smartcard system programmed to allow such transfers.