In music notation, an octave symbol is the characters "8va" or "8bassa" in a small italic font with a dashed bracket continuing to the right of it, drawn just above or below a number of notes and the staff. This symbol indicates that the notes under or over it should be played one octave (twelve half steps) higher ("8va") or lower ("8bassa") than indicated. It's used to keep the number of ledger lines from getting unreadable when more than one or two notes require them.
On the staff, octave symbols look something like this:
8va - - - - -
|
--*-
/\ * |
---| /-------------*-|--|---------------------------------
|/ * | | |
---/-----------|--|--|--|---------------------------------
/| | | | |
-/-|/\---------|--|------------------|--|-----------------
| | | | | | |
|--|--|------------------------|--|--|--|-----------------
\ | | | | | *
--\|_/-------------------------|--|-*---------------------
| | *
\| -*-- |
8bassa - - -