An aura is the essence of your entire being. Anything with sentient life will carry an aura, and it changes their potential interactions with others. Each aura is like a fingerprint, because it is unique to whom it belongs to. An alternate word for an aura is an energy pattern.
The aura is the feeling you give off— the first impression. Though one can choose to project a certain aura, plenty do not go out of their way to change it. An aura influences other sentient beings. The most prominent trait stands out, and compels others to behave in certain ways around the individual. Of course, for anomalies, this is even more intense. An anomaly controls their aura's potency, but it flares with emotions if it isn't kept under control.
The auras of anomalies are far more powerful, and can change the mood of a room. An aura alone could compel a human to think or behave differently. If a human were to enter a room full of anomalies for the first time, they could become overwhelmed and nauseated by the compiling auras. A similar phenomenon might occur at crowds or concerts; auras can cause anxiety, even if they're not from an anomaly.
Human auras are faint and subtle. Most humans are not in tune with their own auras or the auras of others around them on a conscious level. Humans don't have direct control of their auras the way an anomaly does.
A thoughtful anomaly can not only use auras to detect other anomalies nearby, but can also identify who they come from. Auras leave behind a trail that later fades away, and another anomaly could use that to track them down.
Masking an aura isn't difficult, but it can't be held back for extended periods of time. As soon as you utilize energy, your pattern is unmasked.