It is a salvaged card.
By the late 1800's it had become common practice to salvage preprinted postal cards which contained obsolete business messages by coating cards with opaque ink to allow for printing a new address or message. Several companies did this salvage coating as a considerable part of their business. Though not commonly encountered today, here is such an example:

I believe the original poster's card is such an example of a salvaged private card and probably had a preprinted message (salesman will-call notice?) covered up. It may be readable with the right lighting.