Reflexes
'Reflexes' is a Stat that affects various skills requiring you to react fast and be quick and nimble. Reflexes is important to most builds as it effects most weapon skills, dodge, and the speed of melee attacks.
Where to train
Speed bags in various gyms. Brucie's Gym in Corpclave has one that can be set all the way up to difficulty level 8, while Rolf's Gym in Slagtown can only go up to 5.