Some weapon mods, such as Laser Improved Sights, claim to improve your "focus". What is focus, and how does it affect combat?
This is hypothetical and based off info on the wiki, but I think focus relates to the amount of action points used.
If we look at the Laser Pistol table, in the Sights section, we can see that both sights having a bonus to "focus" also decrease the action points cost while all other sights cause an increase:
If we take a detailed look at the Improved sights, which claims to have an increase in 'focus and sighted accuracy', we can see that the only attribute changed is the accuracy, plus the AP cost from the previous table:
Since the only two attributes changed are the accuracy and AP cost, and the weapon claims to change the accuracy and focus, we can deduce that focus is the AP cost.