Here are the Italian terms most used in music theory to designate the dynamics, that is to say the sound volume of the music notes. A kind of decibelmeter in Italian.
The main dynamics you will find on music scores range from pianississimo (ppp) to fortississimo (fff).
Dynamics indications are valid as soon as they are written and until a new indication of dynamic appears.
pianississimo (ppp) : very very soft
pianissimo (pp) : very soft
piano (p) : soft
mezzo piano (mp) : moderately soft
mezzo forte (mf) : moderately loud
forte : (f) loud
fortissimo (ff) : very loud
fortississimo (fff) : very very loud
Dynamics are always written below the staff 
The Dynamics, relatives indications
A dynamic is only an indication and it is relative to its context: For example, piano (p) written for all the violins of a symphonic orchestra is not necessarily the same as piano (p) of a French horn in a wind quintet.Interpreters and conductors must interpret the dynamics in their contexts, and sometimes adapt them to the acoustics of the concert hall.Some composers write on their manuscripts the "exact dynamics they wish to hear", others will trust the performer.Dynamics in the history of music
You should know that in baroque music there were relatively few written dynamics, a little more in classical music and even more in romantic music. And in contemporary music you can sometimes find one dynamic on each note.
How to play and interpret the dynamics
The dynamics must be interpreted in their contexts, a mezzo forte in a string quartet does not necessarily have the same sound volume as a mezzo forte in a symphony for example, and we must also take into account the sound and acoustic from the concert hall.
To put it simply, there can be comparisons with everyday life:
- mezzo forte (mf) can be compared to when you normally speaks to someone.
- forte (f) can correspond to when you speaks to be heard.
- piano (p) can be a conversation in a low voice.
- pianissimo (pp) can be compared to a whisper without using the vocal cords.
