When a message is replied to in e-mail, Internet forums, or Usenet, the original can often be included, or "quoted", in a variety of different posting styles.
The main options are interleaved posting (also called inline replying, in which the different parts of the reply follow the relevant parts of the original post), bottom-posting (in which the reply follows the quote) or top-posting (in which the reply precedes the quoted original message). For each of those options, there is also the issue of whether trimming of the original text is allowed, required, or preferred.
For a long time the traditional style was to post the answer below as much of the quoted original as was necessary to understand the reply (bottom or inline). Many years later, when email became widespread in business communication, it became a widespread practice to reply above the entire original and leave it (supposedly untouched) below the reply.
While each online community differs on which styles are appropriate or acceptable, within some communities the use of the "wrong" method risks being seen as a breach of netiquette, and can provoke vehement response from community regulars.
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