Put simply, dynamics in music refers to its loudness. Musical notation normally includes instructions to let the performer know how loudly or quietly they should play their part. These instructions originally appeared in Italian, and Italian terms for dynamics are still more common than those in other languages.
Dynamics began to appear in music during the Baroque period but were not commonly used until the 18th century.
The most common dynamic instructions found in music are based around the simple terms piano (soft) and forte (loud):
Pianissimo pp Very soft
Piano p Soft
Mezzo piano mp Quite soft
Mezzo forte mf Quite loud
Forte f Loud
Fortissimo ff Very loud
In addition, there are terms to indicate the gradual change of volume, as follows:
Crescendo or cresc. [insert hairpin] Get gradually louder
Diminuendo or dim. [insert hairpin] Get gradually softer.
Sometimes decrescendo is used.
The signs shown above are called hairpins and it is not unusual to see a ‘louder’ hairpin immediately followed by a ‘softer’ one.
Other Italian words are sometimes paired with the above dynamic instructions – e.g. più f would mean ‘louder’:
Molto Very or Much
Non Troppo Not too much
Poco A little
Sometimes ‘fff’ or ‘ppp’ are used to indicate extremes of volume – and in some cases there could be even more duplication.
Sudden changes can be shown in a number of ways (other than subito):
Sforzando or sf can be used to mean ‘forced’.
A > sign above or below a note can show that it is accented.
fp stands for fortepiano and means loud, then immediately soft.
There are, of course, a myriad of other ways in which the composer may indicate volume to the performer, and many do so in their own languages.