Hit
The term Hit refers to an instance of damage dealt from an attacker to a target. The damage can be 0 after mitigations, but never negative.
The damage dealt by hits can be one of 3 damage types: attack, spell or secondary. Damage over time do no hit.
On/when hit effects
On-hit effects include inflicting status ailments, gaining charges, Stunning or knocking back enemies, gaining life or mana, and skill-specific effects like 
Infernal Blow's explosion.
Some effects have specific requirements, such as Module Error: No skills found with q_where = skill.active_skill_name="Life Gain on Hit" only working with attacks, Module Error: No skills found with q_where = skill.active_skill_name="Culling Strike" only affecting enemies with less than 10% life, and 
Voll's ProtectorVoll's Protector
Holy ChainmailArmour: (388-582)
Energy Shield: (82-122)
Movement Speed: -5%Requires Level 35, 53 Str, 53 Int(100-150)% increased Armour and Energy Shield
50% reduced maximum Mana
Gain a Power Charge for each Enemy you hit with a Critical Strike
Inner ConvictionAlthough a great leader during the war,
Voll proved disastrous in times of peace.
's effect needing a critical strike.
A few examples of effects that do not apply on-hit effects:
References
- ↑ Mark_GGG (February 21, 2016). "GGG, can we get some answers on Conversion please?". Path of Exile Forums. Retrieved February 21, 2016.