This symbol is called a bass clef. The bass clef is also placed at the beginning of a music staff for lower (bass) notes.
A staff with a bass clef written on it is called a bass staff.
The lines and spaces on the bass staff are named as follows:
Extra notes can be added by the use of short lines, called ledger lines, e.g.:
As with the treble staff, when the note head is below the middle staff line the stem points upward and when the head is above the middle line the stem points downward. A note placed on the middle line (D) can have its stem pointing either up or down.