1. part; portion; share
良かったら私の分も食べて下さい。If you like, please eat my share too.
2. amount; worth (as in "two days' worth"); enough (for)
まさか全種類を四人分買ったのか？You didn't buy all the varieties for four people, did you?
3. one's means; one's place; one's lot; one's social position
己の分はわきまえているつもりだ。I believe I know my place.
4. one's duty; one's part
5. condition; state (of affairs); extent; rate (as in "at this rate")
見ている分には楽しそうだ。As long as you are only watching, it looks like fun.
6. in proportion to; just as much as; to the same degree
山や森よりも歩きやすい分、体力の消耗も抑えられる。Since it's easier to walk on than mountains or forests, you also use up less stamina.
7. content (e.g. alcohol); percentage
8. equivalent to (e.g. an old brother)