Amp is a hack used by players in New Cap City to boost their reflexes and reaction time. In V-world, amp takes the form of a drug injected into the user's eye via a J-shaped device akin to an asthma inhaler.
Overuse of Amp leads to addiction in the real-world, as it takes more of the drug to achieve the same effect over time, due to the increase in various chemicals and stimuli of the user's brain that translate via the wearer's holoband.
Emmanuelle introduces Joseph Adama to Amp while helping him track down his daughter Tamara's avatar in New Cap City, and he uses it to eliminate the crowd at the Mysteries club after Cerberus expels him (CAP: "Ghosts in the Machine"). Adama begins to overuse the hack, much to his guide's concern (CAP: "End of Line").