Tables that have redundant data have problems known as anomalies.So data redundancy is a cause of an anomaly.
Redundancy is the duplicaion of the data.
There are 3 types of anomalies.
Insert Anomaly:When you insert a record without having it stored on the related record.
Delete Anomaly:When you delete some information and lose valuable related information at the same time.
Update Anomaly: Any change made to your data will require you to scan all records to make the changes multiple time.
I hope this answers your question:)