Post is a generic term for anything you put on social media or a blog. It can also be used as a verb (ie “I posted that on Facebook”).
While the term came from pre-digital communication (ie post meaning mail), it is telling that a post is different to a message in digital. A post is an item that is put somewhere and then left to be read or viewed, while a message (often called a Direct Message or DM online) is between two people.
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