Soul Trap (effect)

Soul Trap is an enchantment which can be applied to to weapons and used to capture the souls of the monsters and NPCs slain and place them in soul gems.

Fiery Soul Trap
Fiery Soul Trap is a two-tiered enchantment found on one particular weapon: the Steel Battleaxe of Fiery Souls. That battleaxe can be disenchanted and the enchantment can then be applied to other weapons.