Economic growth is an increase in a country's real GDP over time. Real GDP is the value of output with the effect of inflation removed, so it shows whether more goods and services are in fact being produced.
Growth comes from a rise in total demand, which uses spare capacity, or from more or better resources, which raises capacity. It can bring higher incomes, more jobs and more tax revenue, but also inflation, pollution, faster use of resources and wider inequality.
A recession is the opposite: real GDP falls for two quarters in a row. Unemployment rises, firms' profits fall, and the government collects less tax while paying more benefits.