A postcard is a card for sending messages by post with an envelope.
Postcards often have a picture or photograph on one side.
Oxford Advanced Learner’s Dictionary (Hornby, 2002)
Here is an example of a postcard:
Kuta, March 20, 2008
Dear Sari,
I arrived in Bali 2 days ago. It is a wonderful place. The beaches are
nice. The hotel is right on the beach. I toured the island yesterday and
brought some souvenirs for friends in Surabaya. I’ll be back on Sunday.
Well, that’s all for now.
Regards for your family.
Love,
Risma