critical strike question

What is the difference between "Critical Strike", "Global Critical Strike", "Critical Strike Multiplier", and "Global Critical Strike Multiplier" ?

Well first of you need to know what damage can crit, like weapon's attack, spell, secondary damage (herald of thunder, herald of ice) and its obviously something that can hit.

Now there is spell crit, attack crit and global crit and something called local crit.

Local critical on weapon can be increased with weapon explicit and implicit modifier.

Local critical chance is called base critical chance and can be modified with additive 'base critical' sources of global base critical chance (hatred watcher eye mod, assasin ascendency pow charge node), conditional mods (like brittle ailment, assassin mark curse, assassins' poison ascendency node) or local based on support gems (Nightblade, inc critical chance) or item modifiers (Essence of Horror on gloves and similar mods on helm) and also attack/spell/specified base crit ( vaal corruption on gloves, cluster jewel for herald secondary damage)

Your 'total base critical' is then modified with increase critical chance mods, to roll critical strike with weapons your accuracy is also important.

For example
//base crit: weapon is 6% x (1 + 25% weapons explicit/100)= 7.5 + 2% inc crit chance form support gem + 1% from corruption on your gloves + 2% assassin mark curse on the boss = 12.5
//total crit chance:
12.5 x (1+(150% from linked support gems + 220% from skill tree + 150% from pow charges + 100% from flask + 60% from inc crit against shocked enemy + 30% from ammulet) /100) = 12.5 x (1+710/100) = 12.5 + 88.75 = 100 crit chance.


Global crit scale all, others are either weapon based or spell based and some are conditional like critical against shocked, curse, blinded, bleeding enemy.

Multiplier is something that increase your damage when you successfully roll critical strike, base critical damage is 150% and all rest is additive (150% + 25% + 10% + 10%).

On successful roll for critical strike you get
hit damage x (crit multiplier %/100)