The term redpill refers to a human that is aware of the true nature of the Matrix. Redpills are typically humans whose bodies and minds have been freed from the power plant by Zion hovercraft teams, but humans still connected to the Matrix can also be aware of its reality. Usually, Redpills encounter anomalies or glitches in the system, or may free themselves from physical bonds by exceeding human limitations. In either of these cases, other Redpills find them and offer them freedom.
The term gets its name from the color of the virtual pill given by a hovercraft operative (who has re-materialized inside the Matrix as an avatar) to a human still living out a life within the Matrix. The pill is actually a tracing program that disrupts the carrier signal of the pod-human's mind, making it possible for a hovercraft operator to locate the pod that holds the human, and sending commands that force it to go offline and awaken its inhabitant.
Humans who suddenly awaken appear to be instantly rejected by docbots, who disconnect them from their pod's umbilicals and eject their body to the old sewer system of the ancient human cities, where the hovercraft crew retrieves the freed human.
It's important to note that resistance members make it a rule to only free someone from the Matrix before they reach a certain age. Removing a bluepill who has lived long enough in the Matrix could be dangerously overwhelming for them to the point that they're driven insane or even suicidal in their inability to adapt to the radically different circumstances of the real world. When Neo is first shown the reality of the Real World and The Matrix, he begins to go into convulsions and Cypher opines that "he is going to pop", suggesting that it is not uncommon for Redpills to die when they find out the truth. There are occasional exceptions to this, such as when Morpheus had to free Neo in spite of Neo's initial denial of the truth, as Morpheus truly believed he was the One.
As part of establishing a new identity, redpills often adopt an alternative single-word alias based on individual preference. This alias can refer to anything, often associated with philosophy, mythology, religion, nature, literature, culture, technology and computer science. A common example of this are redpills who were formally hackers in the Matrix using their hacker screen name as their new name. They may also choose to retain their bluepill names from the Matrix. In either case, Agents still address redpills by their bluepill surname, such as how Agent Smith always refers to Neo as "Mr. Anderson", or Cypher as "Mr. Reagan".
Occasionally, a redpill may wish to return to the ostensibly more comfortable lifestyle within the Matrix despite its illusory nature. While this can be used as a source of manipulation or coercion, as did Agent Smith with Cypher, it is revealed by Agent Gray in The Matrix Online that there is no process for a freed human to be reinserted into a power plant.
Of all of Zion's inhabitants, only humans who are born within the Matrix can become operatives that can re-enter the Matrix, as they have the headjack that allows their minds to be re-transmitted back into the Matrix's broadcast network. Apart from those who self-substantiated, all humans who have escaped the Matrix had to have taken a red pill or something similar. It is believed that a redpill's RSI is different from a bluepill's, enabling Agents to easily track them in sensitive areas.
Upon returning to the Matrix, a redpills awareness of the virtual reality allows them to bend the Matrix's rules and exceed normal physical limitations. It is worth noting that this does require training before it can be perfected. Common abilities that redpills possess while plugged into the Matrix are unnatural speed, strength, agility, jumping exceedingly far, and other enhanced attributes that seem to defy the laws of physics. Redpills also have access to certain resources, such as skills that have been downloaded into their minds or weapons and equipment generated by a real-world operator. However, no redpill (save the One) has ever been able to match an Agent in combat.