You have practiced extensively with a variety of weapons, giving you the following options:

You get 5 mastery points, that you can spent when taking this feat:

• Training: You can spend one mastery point to gain proficiency with one simple or martial weapon.
• Blocking: You can spend two mastery points to gain the ability to add a +1 to your AC, as a reaction to a melee attack, alternatively you can perform a counterattack, reducing the damage dealt to you by your weapon damage. You can use this ability equal to half your player level rounded up and again after a long rest.
  Ability only applies, when wielding a chosen simple or martial weapon you're proficient with and not wearing a shield.
• Perfection: You can spend three mastery points to gain temporary expertise with one simple or martial weapon you're proficient with, doubling the proficiency bonus to hit.
  This expertise lasts for 5 subsequentive turns after your first hit in a combat.
• Universal: You can spend all five mastery points to gain half proficiency (Just adding half your proficiency bonus) to every simple or martial weapon you wield.