What are top-posting and bottom-posting?

Top-posting and bottom-posting are terms that refer to where a response to a text-message appears in a thread of messages. Top-posting means that the reply appears above the message that is being answered. This allows the new content to be seen at the top of a message. Bottom-posting means the response is beneath the original message. This allows a message to be read top-to-bottom. Bottom-posting is the accepted standard when posting responses to messages via Usenet.