der Kofferraum
trunk
The storage space in a car, usually located at the rear, used for transporting luggage, groceries, and other items.
Wir haben alle Koffer im Kofferraum verstaut.
We stored all the suitcases in the trunk.

trunk
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trunk
The storage space in a car, usually located at the rear, used for transporting luggage, groceries, and other items.
Wir haben alle Koffer im Kofferraum verstaut.
We stored all the suitcases in the trunk.

'Kofferraum' (trunk) is made up of 'Koffer' (suitcase) and 'Raum' (space/room). So it is literally the 'space for suitcases' in a vehicle.
Der Kofferraum dieses Kleinwagens ist überraschend groß.
The trunk of this small car is surprisingly large.
Pay attention to the case with the preposition 'in': movement into the storage space is expressed with the accusative ('in den Kofferraum' - into the trunk), while a state/location inside it is described with the dative ('im Kofferraum' - in the trunk).
Bitte leg die Einkaufstüten in den Kofferraum.
Please put the grocery bags into the trunk.
Common verbs used with 'Kofferraum' (trunk) are 'öffnen' (to open), 'schließen' (to close), 'etwas hineinlegen' (to put something in), 'etwas herausnehmen' (to take something out), or 'beladen' (to load).
Kannst du bitte den Kofferraum öffnen?
Can you please open the trunk?
rear / stern
'das Heck' and 'der Kofferraum' are easy to confuse because in many cars the trunk is at the rear. But 'Heck' means the rear part of a vehicle in general, for example the back of a car, ship, or airplane. 'Kofferraum' means only the storage space in a car where you put luggage, groceries, or other things. If you are talking about damage or the shape at the back of the vehicle, 'Heck' fits. If you are talking about luggage or storage space, 'Kofferraum' fits.

Vor der Reise haben wir alle Taschen in den Kofferraum gelegt.
Before the trip, we put all the bags in the trunk.
Beim Einparken wurde das Heck des Autos leicht beschädigt.
While parking, the rear of the car was slightly damaged.