Agents can become cloaked by using a Cloaking Rig or the Subdermal Cloak augment. While cloaked, the agent is invisible to the enemy, meaning they can walk through enemy vision without being noticed, seen or overwatched.
Cloaked agents cannot be seen by guards, Security Cameras or Turrets. However, any noise made by a cloaked agent can still be heard by guards, and a cloaked agent can still be detected by a drone's Local Scanner or by a Pulse Drone's scan.