manual/include/the-tracks-and-busses-list.html

<p>
  This lists the tracks and busses that are present in the session. The list order
  reflects the order in the editor, and track or bus names can be dragged-and-dropped
  in the editor list to re-order them in the editor. The columns in the list
  represent the following:
</p>

<table class="dl">
  <tr><th id="visible">V</th>
  <td>whether the track or bus is visible; they can be hidden, in which case they
    will still play, but just not be visible in the editor; this can be useful for
    keeping the display uncluttered.</td></tr>
  <tr><th id="active">A</th>
  <td>whether the track or bus is active; inactive tracks will not play, and will
    not consume any CPU.</td></tr>
  <tr><th id="input">I</th> <td>for MIDI tracks,
    whether the MIDI input is enabled; this dictates whether MIDI data from the
    track's input ports will be passed through the track.</td></tr>
  <tr><th id="record">R</th> <td>whether the track is record-enabled.</td></tr>
  <tr><th id="record-safe">RS</th> <td>whether the track is record safe; a record safe
    track cannot be armed for recording, to protect against a mistake.</td></tr>
  <tr><th id="mute">M</th>
  <td>whether the track is muted.</td></tr>
  <tr><th id="solo">S</th>
  <td>track solo state.</td></tr>
  <tr><th id="solo-isolated">SI</th>
  <td>track solo-isolated state.</td></tr>
  <tr><th id="solo-safe">SS</th>
  <td>solo safe state. </td></tr>
</table>

<p class="note">
  Each icon in these columns can be clicked to toggle the track/bus state, which
  is a very fast way to set multiple tracks/busses state at once.
</p>

<p>
  As with the region list, hovering the mouse pointer over a column heading shows
  a tool-tip which can be handy to remember what the columns are for.
</p>