This skill lets you do more damage with polearms and parry with them more reliably. Note that no level of mastery will let you do great damage with mundane weapons.
The ingame help reads:
Skill duration: random. Type of skill : weapon skill. Affecting stats: Str/Dex. It uses no endurance points. Weapons ranging from long spears, to halberds and pikes, all fall under the category of polearms. While not as commonly seen as a sword or an axe, they are still effective weapons. Due to their size and abilities they are most commonly found in large organized armies. Ineffective for close in fighting and skirmishing, they are prefered usually for large scale battles involving hundreds or thousands. They are effective when used in great numbers, being able to create an impenetrable wall. Their great length also makes them ideal for either using on horseback, or using from the ground to counter foes on horseback. A great deal of skill is required to use these weapons effectively. Knowing when to feint and thrust can make all the difference in sticking your foe in the chest, or thrusting into open.