I’m writing this because I just found out recently myself. I had heard the term used frequently by stationers, but decided to educate myself more on the topic.
Many of us know what engraving is (the practice of etching a design into hard surfaces, such as plaques, jewelry, dog tags, etc.). Letterpress also involves the relief printing of letters, creating impressions on paper.
However, thermography is the opposite – it is a type of raised printing. I became curious about it after being asked to do handwritten calligraphy with ink on envelopes on which the return address had been done this way. According to Wiki, thermographic printing “refers to two types of printing, both of which rely on heat to create the letters or images on a sheet of paper. The simplest type is where the paper has been coated with a material that changes color on heating. This is called thermal printing and was used in older model fax machines.” There seems to be quite a science to it, but here you can see an example of the outcome, specifically for use on invitations, business cards, and the like:
(Photo courtesy of Tiny Prints: the link to the blog page is here)
If you too were ever curious about this type of printing, now you know! 😉