What are long-term means?

Long-term means are the twenty year averages which were computed for our four time periods; Near Term (2020-2039), Mid-Term (2040-2059), End of Century (2080-2099), Last Decade (2090-2099). As well as our present day twenty-year average which is computed from the 20th Century Experiment (1980-1999). We use a twenty-year average to compute our anomalies in order to filter out noise from the model and better see the climate signal.