From The Collaborative International Dictionary of English v.0.48 :
Sforzando \Sfor*zan"do\, Sforzato \Sfor*za"to\, a. [It.
sforzando, p. pr., and sforzato, p. p. of sforzare to force.]
(Mus.)
Forcing or forced; -- a direction placed over a note, to
signify that it must be executed with peculiar emphasis and
force; -- marked fz (an abbreviation of forzando), sf, sfz,
or ?.
[1913 Webster]