Ledger lines are short lines added above or below the staff for notes that fall outside it. An octave sign does the same job differently: 8va above the notes means play an octave higher, 8vb below means an octave lower.
Five lines cover about an octave and a half. A piano has more than seven. So notation needs a way to write notes outside the staff, and there are two — the same problem at two different scales.
One ledger line, three, five. The more you count, the slower you read.
A ledger line or two costs nothing. Past the fourth you are counting lines instead of recognizing a note, and that is exactly what 8va is for: put the notes back inside the staff and say separately that they sound an octave higher.
Sign
Written
Means
8va
Above the notes
Play an octave higher
8vb (or 8va bassa)
Below the notes
Play an octave lower
15ma / 15mb
Above / below the notes
Play two octaves higher / lower
loco
At the end of the dashes
Back to written pitch
Common questions
What does 8va mean?
It is short for ottava, Italian for octave. Notes under the dashed line are played one octave higher than they are written, which saves reading a pile of ledger lines. Where the line ends, the written pitch applies again.
What do 8vb and 15ma mean?
8vb is the same sign below the notes and means one octave lower. 15ma, short for quindicesima, means two octaves higher, and 15mb two octaves lower; the dashed line shows how far each one reaches.
How do you count ledger lines quickly?
Learn the first ledger line above and below each staff as landmarks: on the treble staff, A above and C below. Each further line is a third away, so skip a letter each time: A, C, E, G going up and C, A, F going down.