Anomaly Definition
If you are a game player you would definitely make this term a glitch in matrix and you are right but in terms of software development we all gathered for anomaly is sentry at gate or manipulating if you want, fraudulent activities that warn developers about possible errors, to put it simple imagine you have a film-alike console and anomaly is sudden blip on radar that identifies something is wrong with system.
They can be hidden in plain sight across noisy datasets so you may have implement machine learning and AI practices to increase identification process efficiency to separate wheat from chaff when it comes to anomaly detection and understanding.