Fetching details from the dictionary...
stain; spot; smudge; blot; smear; blotch
spot (on one's skin, e.g. chloasma, liver spot); blemish; discoloration; freckle
シャツに染みがある。
There is a stain on the shirt.
この染みは落ちない。
This stain won't come off.
彼の服には大きな染みがあった。
There was a big stain on his clothes.