‘Keep me posted’ is an idiom implying that one person will keep another up-to-date with information on a particular situation.
It could have several origins. For instance, the earliest Old English use denoting a long stick of wood was taken from the Latin term “postis” of the same meaning. Gradually a ‘post’ began to refer to both the pole on which the sign was erected and the sign itself.
During the Colonial Era, if someone wanted to share news or information with the community, the person would post a note on a large wooden post. The wooden post usually was in a central area where people gathered for conversation or gossip.
In Middle English the term came to mean displaying news or names in a public forum. For example, ‘posting banns,’ for a couple planning to marry or publicly denouncing someone as ‘posted.’ Again, trespassing signs evolved during this period, and it was said that a property was ‘posted.’
The term has been adopted on the Internet, as in ‘posting a reply,’ a ‘post’ or even the ‘repost’ of a message. Indeed, the Internet and electronic posts have allowed people to ‘keep posted’ and up to date on news and information at a faster rate than printed posts or ‘snail mail.’
The term may also be related to ‘post office’ or ‘postal mail.’ A combination of the Old French ‘poste’ and the Old Italian ‘posta’ meaning “a relay station for horses, with Vulgar Latin ‘posta’ meaning “a station” certainly relates to the transportation of mail along a given route. Perhaps, in early American history, the full name of the pony express was ‘the pony express post.’
There is a product manufactured by the Scotch tape people, called “Post-it.” It’s a pad of square colored paper, one end of which has glue attached to it. You can write notes on the paper and then stick it to any surface. The name itself is a pun on the verb ‘post.’ This enables you to “post a Post-it”.
Post-its can even help you with future events, in effect, keeping yourself posted. Just write “pick up books at library” on a Post-it note, and slap it on the fridge. There — you’ve got the news before it’s even happened!