The Diablo 2 Wiki
The Diablo 2 Wiki archive is available for anyone looking for information on Diablo 2. All information here is pre-D2R but contains a lot of useful information that is still relevant. Updated sections for new D2R features can be found on the PureDiablo Diablo 2 section

Demon Heal

From Diablo 2 Wiki

Demon Heal is a fairly useless special modifier added in the Expansion. It's found only on Crafted Items.

Demon Heal adds some small amount of hit points (generally 1-3) for every Demon (as opposed to an Animal or Undead) you kill. There is no Animal Kill or Undead Kill modifer.