Axe Specialization is one of the racial traits granted to all orc characters. It grants an expertise bonus while using axes or fist weapons. When dual wielding different types of weapons, Axe Specialization is applied to each weapon individually, so that if you dual wield an axe and a sword, only attacks made with the axe benefit from Axe Specialization. If you instead dual wield an axe and a fist weapon, all of your attacks will benefit from Axe Specialization. For attacks that only use the mainhand weapon, such as a rogue's Sinister Strike, only your mainhand expertise matters.