Medium Armor Master
Source: Player's Handbook
Prerequisite: Level 4+, Medium Armor Training
You gain the following benefits.
Ability Score Increase. Increase your Strength or Dexterity score by 1, to a maximum of 20.
Dexterous Wearer. While you're wearing Medium armor, you can add 3, rather than 2, to your AC if you have a Dexterity score of 16 or higher.