Transfer baggage refers to checked baggage carried on two or more connecting flights and that has to be moved from one plane to another.
You can check in baggage for connecting flights provided that all your flights have the same record locator or booking reference. In most cases, your baggage will be tagged to go straight to your final destination (you can check this on the baggage tag receipt you get when you check it in), but you will have to collect it and check it in again for your connecting flight if:
The flights are in separate bookings.
You are transferring from an Iberia flight to a domestic flight in a country where the local authority requires you to collect your baggage and go through customs (e.g. in the United States or Mexico).
You arrive at one airport in the destination city and your connecting flight leaves from another airport in the city.
Your connecting flights are not on the same day and the total transfer time exceeds 12 hours.
Part of the journey is by bus or train.
You should enquire at the departure airport where you will need to pick up your baggage.
Transits at T4 at Madrid airport.