Gradual Changes in Volume
Sometimes a composer may want the music to get gradually louder or gradually softer. The two most common terms are crescendo, sometimes abbreviated to cresc., meaning “get gradually louder”; and decrescendo or diminuendo, sometimes abbreviated to decresc. or dim., meaning “get gradually softer”. Signs, sometimes called “hairpins,” are also used to stand for these words.
These are made up of two lines that connect at one end and get gradually further apart. If the lines are joined at the left, then the indication is to get louder; if they join at the right, the indication is to get softer.