A clef is a symbol used to assign a specific pitch to one of the five lines of a stave, thereby also indicating the pitches of the other lines and spaces. The four clefs in common use today make it possible to write music comfortably on staves with a minimum of ledger line for all instruments and voices, regardless of differences in their ranges. A clef is always placed at the very start of each stave, to the left of the key signature and time signature, as well as at the start of any location in a score where there is a change from one clef to another.
The most familiar of the four commonly used clefs today, is the treble clef, which resembles an elaborate ampersand and and is often used as a symbol representing music in general. It is placed so that the midpoint of the large loop near its bottom is on the G above middle-C, which is the second line from the bottom on any stave on which it is used. This clef is usually used on the upper of the two staves for piano sheet music and is also usually used for many other instruments that do not produce predominantly low pitches, such as the flute, oboe and violin.
The second most commonly used clef is the bass clef, which resembles a large, reversed letter C with two dots vertically aligned to its immediate right. It is placed so that the two dots are just above and below the F line, which is the second from the top line on any stave on which it is used. This clef is usually used on the lower of the two staves for piano sheet music and is also usually used for other instruments that produce predominantly low pitches, such as the bassoon, trombone and cello.