manual/include/working-with-markers.html

<p>
  It is very useful to be able to tag different locations in a session for
  later use when editing and mixing. Ardour supports both
  <dfn>locations</dfn>, which define specific positions in time,
  and <dfn>ranges</dfn> which define a start and end position in time.
</p>
<p>
  In addition to the standard location markers, there are three kinds of
  special markers:
</p>
<ul>
  <li>
    <dfn>CD markers</dfn> are locations that are restricted to legal
    <dfn>CD sector boundaries</dfn>. They can be used to add track index
    markers to compact disc images.
  </li>
  <li>
    The <dfn>Loop range</dfn> defines the start and end points for Looping.
  </li>
  <li>
    The <dfn>punch range</dfn> defines the in and out points for punch
    recording.
  </li>
</ul>