der Beifahrersitz
passenger seat
The seat in a vehicle that is directly next to the driver's seat.
Sie legte ihre Handtasche auf den leeren Beifahrersitz.
She put her handbag on the empty passenger seat.

passenger seat
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passenger seat
The seat in a vehicle that is directly next to the driver's seat.
Sie legte ihre Handtasche auf den leeren Beifahrersitz.
She put her handbag on the empty passenger seat.

The word is composed of three parts: 'Bei-' (beside, with), 'Fahrer' (driver), and 'Sitz' (seat). So it is literally the seat located next to the driver.
Der Beifahrer ist für die Navigation zuständig.
The passenger is responsible for navigation.
Pay attention to the case after the preposition 'auf' (on). 'Auf dem Beifahrersitz' (on the passenger seat, dative) describes a position, while 'auf den Beifahrersitz' (onto the passenger seat, accusative) describes movement.
Mein Rucksack liegt auf dem Beifahrersitz.
My backpack is on the passenger seat.
Common verbs used in connection with the passenger seat are 'sitzen' (to sit), 'sich setzen' (to sit down), and 'etwas legen' (to put something down).
Er setzte sich auf den Beifahrersitz und schnallte sich an.
He sat down in the passenger seat and fastened his seat belt.
back seat
'Beifahrersitz' and 'Rücksitz' both refer to seats in a car or another vehicle. The difference is the position: the 'Beifahrersitz' is at the front, directly next to the driver's seat. The 'Rücksitz' is in the back, usually the rear bench seat. The words can be confused because both seats are for passengers and not for the person at the wheel. If someone is sitting in the front next to the driver, you say 'Beifahrersitz'. If someone is sitting in the back, you say 'Rücksitz'.

Amira legt ihre Tasche auf den Beifahrersitz, bevor sie einsteigt.
Amira puts her bag on the passenger seat before getting in.
Die Kinder schlafen auf dem Rücksitz, während die Eltern nach Hause fahren.
The children are sleeping on the back seat while their parents drive home.