In music, the dynamics of a piece is the variation in loudness between notes or phrases. Dynamics are indicated by specific musical notation, often in some detail. However, dynamics markings still require interpretation by the performer depending on the musical context: for instance, the forte marking f (meaning loud) in one part of a piece might have quite different objective loudness in another piece or even a different section of the same piece. The execution of dynamics also extends beyond loudness to include changes in timbre and sometimes tempo rubato.

The two basic dynamic indications in music are:

p or piano, meaning "quiet".

f or forte, meaning "loud or strong".

More subtle degrees of loudness or softness are indicated by:

mp, standing for mezzo-piano, meaning "moderately quiet".

mf, standing for mezzo-forte, meaning "moderately loud".

più p, standing for più piano and meaning "more quiet".

più f, standing for più forte and meaning "more loud".

More Info: en.wikipedia.org