Accelerando, accel. If the pulse of a piece of music is to become gradually quicker the word ACCEL. (short for accelerando) is used. A dotted line shows how long the acceleration is too last, and 'A tempo', or tempo 1, meaning 'primo', is written when the pulse returns to its original speed.
Ad Libitum / Ad Lib. a tune meant to be sung or played very freely, without any regular pulse. They are written without any time signature or bar lines. The word 'freely' can be written Ad Libitum (or Ad lib.) meaning 'at will'.
The style and speed of the music is left for the player or singer to decide.
Bar / Measure 'distance in time', between one bar line and the next (Americans call a bar a Measure).
The lines are the vertical strokes showing where the first pulse occurs in the new bar.
Rhythm all tunes have rhythm. Sometimes the rhythm is free flowing, but more often it is measured with a regularly occuring Pulse. The pulse is not like the ticking of a clock: there is a physical tension and relaxation in it. Unfortunately, we often lose this effortless continuity when learning to 'keep time' in music. In the early stages of keeping time, a measured rhythm can be Counted where each syllable is given a rhythmical pattern of long notes and short notes.
