Here are some common musical terms.
accel. (accelerando) = gradually speeding up
Allegro = quick and lively
Allegretto = fairly quick, but not as fast as Allegro
Andante = at a walking pace
calando = dying away
cresc. (crescendo) = becoming gradually louder
D.C. (Da Capo) = repeat from the beginning
dim. (diminuendo) = becoming gradually softer
decresc. (decrescendo) = becoming gradually softer
D.S. (Dal Segno) = repeat from the sign
f (forte) = loud
ff (fortissimo) = very loud
largo = large or grand
lento = slowly
m (mezzo) = lit. "half", i.e. medium, so mp, medium soft and mf, medium loud
moderato = at a moderate speed
morendo = dying away
p (piano) = soft
pp (pianissimo) = very soft
presto = fast
prestissimo = as fast as possible
rall. (rallentando) = gradually slowing down
rit. (ritenuto) = slower
tenuto = hold
vivace = lively