What is Postcard?

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