Estoc (5e Equipment)
From D&D Wiki
Martial Melee Weapons
The estoc was a variation of the longsword designed for fighting against mail or plate armor. It was long, straight and stiff with no cutting edge, just a point. Blade cross-sections can be triangular, square, rhomboid or flat hexagonal. This geometry left hardly any cutting capability as a sharpened edge could simply not be ground, but allowed the weapon to become lengthy, stiff, and very acutely pointed.
When you attack a creature wearing heavy armor with an estoc, that creature has a -2 AC penalty for the duration of the attack.