Several roles (most notably X-Shot on an otherwise passive role) can easily be interpreted in two ways: as a role that triggers when it would have some effect, or as a role that is activated by the player. The version that triggers automatically is typically interchangeably referred to as reflexive or passive (which are both correct descriptions, and which are both sufficient to deduce which version of the role is in use, leading to "passive" and "reflexive" often being conflated). The variant which has to be used intentionally is, by contrast, an Activated (thus active) role.
Some roles are inherently reflexive, due to their nature; the best example is Diplomat, which triggers only in response to an elimination, and which tends to be very obvious when it does trigger. However, Reflexive is also sometimes seen as a role modifier (in which case it tends to be spelled with an uppercase R), changing an existing role so that it triggers when the player is targeted (and targets the targeter), rather than being able to be used normally. (Reflexive roles are sometimes named as a Water Carrier, especially in Werewolf flavour.) The most commonly seen example of this is the Reflexive Vigilante, a role seen commonly enough to have its own name (Paranoid Gun Owner). Other common examples include a Reflexive Doctor (or Healing Water Carrier), and the Reflexive CPR Doctor (which is basically just a cross between a Reflexive Doctor and a Paranoid Gun Owner). Other combinations are certainly possible – for example, a Reflexive Cop would learn which factions had targeted them – but tend to be less useful.