At least as it applies to my USR Sword & Sorcery campaign. The Equipment List includes some weapons, such as the flail, which come with a "first strike" attribute.
First strike weapons allow a character to make an initial melee attack without their opponent being able to inflict any damage against them, even if they win the contested attribute roll. This initial attack roll is made in conjunction with the character's regular Action roll for the combat round, in effect, giving the first strike weapon two attack rolls versus your opponents one.
Once engaged in melee a character cannot make a first strike attack. If two or more characters are attacking each other with first strike weapons, no one can make a first strike attack.
First strike does not apply to ranged weapon attacks.