What is the meaning behind bass clef lines and spaces?

The bass clef staff is a lower register than the common treble clef; where the treble clef places middle C one ledger line below the staff, the bass clef places middle C one ledger line above the staff. The lines and spaces represent different notes for the instrument to play.

Starting from the bottom of the staff, the bass clef line notes are G, B, D, F and A. This leaves the spaces as A, C, E and G. Common mnemonic devices to remember these notes are "Good Boys Do Fine Always" and "All Cows Eat Grass." Bass clefs, when playing the concert B flat scale, start an octave lower at B flat on the second line on the staff.