What kind of damage it is

spell damage
Damage that came from a spell, whatever it is made of.

auto-attack damage
Damage that came from an attack rather than a spell.

magic damage
Damage of any type except physical. A physical spell is spell damage but not magic damage.

damage over time
Damage dealt in ticks over a duration rather than all at once. Ticks behave differently from hits - they never critically hit and never leech.

lifesteal
Heals you for a share of the damage you dealt, every hit, with no roll. More damage means more healing.

life leech
A chance to heal you for a flat amount. The heal does not grow with your damage.

manasteal
Returns a share of the damage you deal as mana, every hit, with no roll. Damage over time does not count.