Staff and clef - By guitarelements.com

A staff in Notation normally consists of 5 parallel horizontal lines.
The position of a notehead on a staff determines its pitch: a notehead can be notated either against or through lines.

Special notation, such as for percussion, can also employ staves consisting of a different number of lines, even only of 1 line.

At the beginning of most staves a Clef is used to determine its exact usage and to determine the pitches of notated.

A Clef " means key "determines which Pitches are notated on a Staff.

Staff lines and ledger lines

The staff lines are numbered upwards, starting with the lowest line:

This numbering is used when describing notation orally, in spoken language, but can also occur in descriptive writing.

Notes outside the staff are notated with the help of (one or multiple)ledger lines.

Ledger lines are small horizontal lines that act as a local extension of the staff at the position of the note, as can be seen in the next example,
which shows all the steps in basic tones in a four octave scale:

Commonly used clefs

The following four clefs for notating pitch are still in use today, but many more historical clefs can be encountered in older sheet music.

• TheG clef (sometimes also called violin- or treble clef) is used for most woodwind instruments, violin and the middle-high register in general. 
  Middle C is notated on one ledger line below the staff.
• The F clef (also called bass clef) is used for low instruments, such as cello, double bass, bassoon and trombone, and the low register in general.
  Middle C is notated on one ledger line above the staff.
• The C clef can occur on the third or fourth line:
  • On the third line it is called alto clef and used for viola and alto-trombone exclusively.
  • On the fourth line it is called tenor clef and used for the middle-high register of low instruments, such as the cello, double bass and trombone.
  • In both cases, middle C is notated on the (middle) line where the clef is put.

 .