Dynamic song here is a sense of power, which is when they sing or play music should pay attention to the power of each tone. Maybe in certain parts need to be sung / played strong and the other part was sung / played with more subtle. Hard soft on a song called dynamic song. Dynamic track is determined by several factors, one of which is the term dynamic. The term dynamic is in the form of letters stands. If such an image is called dynamic marks.
Basically there are two dynamic terms, forte = strong, and piano means soft. Forte shortened to f, while the piano shortened to p. Abbreviation is always written in lower case. Regarding the strong and soft, there are several levels, namely:
f = strong
ff = stronger than f
fff = stronger than ff
mf = somewhat strong, or less powerful than the f (mezzo forte)
p = soft
pp = softer than the p
ppp = softer than pda pp
mp = slightly soft, or less soft than the p (mezzo piano)
cresc (crescendo) = the longer the stronger.
decresc (decrescendo) = the longer the more tender.
The sign for the crescendo and decrescendo expressed in the picture: