This is the 10294th most frequent German word.
postkarten
Postkarten: postcards.
Here, 'Postkarten' is used as a plural noun indicating the items purchased.
Ich habe während meines Urlaubs viele Postkarten gekauft.
I bought many postcards during my vacation.
In this sentence, 'Postkarte' is singular and refers to a specific postcard received.
Das ist eine Postkarte, die ich von meinem Freund erhalten habe.
This is a postcard I received from my friend.
Here, 'Postkarten' is used to refer to multiple postcards that need to be picked up.