In dynamics music notation, forte is abbreviated 'f' and indicates that the music from that point on should be, well, loud. The word simply means "loudly" in Italian.
When added to the staff, it looks something like this (complete with eigth notes):
/\
---| /----------------------------------------------------
|/
---/---------------*---------*---------*---------*--------
/| | | | |
-/-|/\--------*---|-----*---|-----*---|-----*---|---------
| | | | | | | | | | |
|--|--|------|----|----|----|----|----|----|----|---------
\ | | |____|____|____|____|____|____|____|
--\|_/----------------------------------------------------
|
\| f