The phrase "average anomaly" refers to the difference between a value and its average. It helps us to understand how much something varies from its usual or expected value. Full definition
The Australian and regional seasonal and annual anomalies are calculated as arithmetic averages of their respective monthly average anomaly. (bom.gov.au)
The period of increased warming from 1987 to 1997 loosely coincided with the divergence of the global average temperature anomalies over land, which are derived from observation station recordings, and the global average anomalies in sea surface temperatures. (c3headlines.com)
For each data set, we calculated what the temperature anomaly was in degrees Fahrenheit relative to the 1961 - 1990 baseline, and then averaged the anomalies of all three data sets. (climatecentral.org)