Lethality

You critically hit more often with weapons.
You deal more damage with critical hits with weapons.

Critical Hit:
When you roll a natural 20 on a roll to hit with an attack, you score a critical hit, sometimes also referred to as a crit.
The attack automatically hits, regardless of enemy AC, and the number of any damage dice for that hit gets doubled.
(ex: If you swing a greatsword with Bear Strength which deals 1d12 +1d4 +3 slashing damage normally, on a critical hit, it would deal 2d12 + 2d4 +3 slashing damage.)

Critical Threat Range:
Critical threat range makes you crit more often.
Critical threat range lowers the minimum you need to roll on a d20 to threaten a critical hit. For example, if you have -1 to the number you need to roll to threaten a critical hit, you will crit, dealing damage with double the amount of dice, if you roll either a natural 19 (and the critical is confirmed) or a natural 20.

Critical Confirmation:
If your roll to hit threatens to crit and ties or beats the enemy’s AC, it is actually a critical hit.
If your roll is less than the enemy AC, the attack misses instead.
Natural 20s are always critical hits.

Extra Damage on a Critical Hit:
A critical hit doubles the number of damage dice as part of its normal effect.
This damage is of the same damage type as a weapon or ability’s base type (ex: a slashing weapon deals extra slashing damage on a critical hit) if no damage type is explicitly specified.