A postcard is a piece of card, often with a picture, used for sending messages through the post without an envelope.
postcard (n.) - A piece of thin card, often with a picture on one side, which you can write on and send to people without using an envelope. It is also called a picture postcard, and it is a common way to send short messages or greetings.
;明信片 A postcard is a piece of thin card, often with a picture on one side, which you can write on and send to people without using an envelope.
Oxford
post·card/ˈpəʊstkɑːd; NAmEˈpoʊstkɑːrd/(alsocard)nouna card used for sending messages by post without an envelope, especially one that has a picture on one side 明信片◆colourful postcards of California五颜六色的加利福尼亚州明信片◆Send us a postcard from Venice!从威尼斯给我们寄张明信片来!◆Send your answers on a postcard to the above address.把答案写在明信片上,寄到上述地址。☞see also