Slowing down the spread of a virus to lower the peak ( highest) number of cases so that demands on hospitals and healthcare systems are reduced. Also, see the epidemic curve. As the virus is brought under control the curve will flatten to show this.
During the COVID-19 pandemic mitigation or intervention strategies such as lockdowns and prevention measures such as physical distancing have been introduced to achieve a flattening of the curve.
Epidemiology Infectious Disease Prevention