明信片，一种专供书写文本，不必封函，即可交邮局寄递的邮件。其正面为信封的格式，反面具有信笺的作用。优点是省贴邮票和不用信封，缺点是篇幅小而无隐密性。亦称为「邮片」。明信片所写的内容公开，可被他人所看见，内容通常不涉及隐私权之虞，故称为明信。在某些地方明信片邮资较普通信函资费便宜。依据**中华邮政业务说明，一般民众可自行印制明信片但不得标志「****邮政」，而中国大陆的中国邮政亦有类似规定，因此许多人会称邮局发行之明信片为「邮政明信片」（postal card，带邮资符），而民间印制者则以泛称之「明信片」（postcard）指称。

A postcard or post card is a rectangular piece of thick paper or thin cardboard intended for writing and mailing without an envelope. Shapes other than rectangular may also be used. There are novelty exceptions, such as wood postcards, made of thin wood, and copper postcards sold in the Copper Country of the U.S. state of Michigan, and coconut "postcards" from tropical islands.