A ledger line or leger line is musical notation

Musical notation

Music notation or musical notation is any system that represents aurally perceived music, through the use of written symbols.-History:...

 to notate pitches above or below the lines and spaces of the regular musical staff. A line slightly longer than the note head is drawn parallel to the staff, above or below, spaced at the same distance as the lines within the staff (see Figure 1).

Notes more than three or four ledger lines above or below the staff are usually considered hard to read. When there are many notes in a passage requiring more than three ledger lines, it is often preferable to switch clef

Clef

A clef is a musical symbol used to indicate the pitch of written notes. Placed on one of the lines at the beginning of the staff, it indicates the name and pitch of the notes on that line. This line serves as a reference point by which the names of the notes on any other line or space of the staff...

 or use 8va notation. Some transposing instrument

Transposing instrument

A transposing instrument is a musical instrument for which written notes are read at a pitch different from the corresponding concert pitch, which a non-transposing instrument, such as a piano, would play. Playing a written C on a transposing instrument will produce a note other than concert C...

s, such as the piccolo

Piccolo

The piccolo is a half-size flute, and a member of the woodwind family of musical instruments. The piccolo has the same fingerings as its larger sibling, the standard transverse flute, but the sound it produces is an octave higher than written...

, double bass

Double bass

The double bass, also called the string bass, upright bass, standup bass or contrabass, is the largest and lowest-pitched bowed string instrument in the modern symphony orchestra, with strings usually tuned to E1, A1, D2 and G2...

, guitar

Guitar

The guitar is a plucked string instrument, usually played with fingers or a pick. The guitar consists of a body with a rigid neck to which the strings, generally six in number, are attached. Guitars are traditionally constructed of various woods and strung with animal gut or, more recently, with...

, and the tenor voice, transpose at the octave to avoid ledger lines.

Players of certain instruments prefer ledger lines to clef changes or 8va notation. Clarinet

Clarinet

The clarinet is a musical instrument of woodwind type. The name derives from adding the suffix -et to the Italian word clarino , as the first clarinets had a strident tone similar to that of a trumpet. The instrument has an approximately cylindrical bore, and uses a single reed...

ists, for example, would rather read ledger lines in the chalumeau register than read bass clef notes. Flute

Flute

The flute is a musical instrument of the woodwind family. Unlike woodwind instruments with reeds, a flute is an aerophone or reedless wind instrument that produces its sound from the flow of air across an opening...

 players would rather read ledger lines for notes in the third octave

Octave

In music, an octave is the interval between one musical pitch and another with half or double its frequency. The octave relationship is a natural phenomenon that has been referred to as the "basic miracle of music", the use of which is "common in most musical systems"...

 than read 8va notation because higher flute notes require different fingerings. Tuba

Tuba

The tuba is the largest and lowest-pitched brass instrument. Sound is produced by vibrating or "buzzing" the lips into a large cupped mouthpiece. It is one of the most recent additions to the modern symphony orchestra, first appearing in the mid-19th century, when it largely replaced the...

, trombone

Trombone

The trombone is a musical instrument in the brass family. Like all brass instruments, sound is produced when the player’s vibrating lips cause the air column inside the instrument to vibrate...

, and euphonium

Euphonium

The euphonium is a conical-bore, tenor-voiced brass instrument. It derives its name from the Greek word euphonos, meaning "well-sounding" or "sweet-voiced"...

 players in the instruments' lower register generally prefer ledger lines below the bass staff to 8vb notation or an octave-lowered bass clef for similar reasons.

When music for bass clef instruments, such as the cello or trombone, goes several ledger lines above the bass clef, the tenor clef is used; if it were to go even higher than practical in tenor clef, the notes may be notated in treble clef. Notice, the alto clef is not used in these situations.