ledger line

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A short line placed above or below a staff to accommodate notes higher or lower than the range of the staff.

from The Century Dictionary.

• noun In angling, an arrangement of fishing-tackle in which the lead rests on the bottom.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A musical notation to inscribe notes outside the lines and spaces of the regular musical staves; a line slightly longer than the note is drawn parallel to the staff, above or below, spaced at the same distances as the notes within the staff.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a short line; a notation for extending the range above or below the staff