The number (range) of cases of a disease that one would expect to occur in a given popuation group if population and environmental conditions are stable.o Expected frequency (normal expectancy) is derived by looking at average of number of cases of the disease in previous 3 -- 5 years in that geographical area.Other terms related to endemic disease : -i) Hyperendemic -p The disease is constantly present at a high incidence and/or prevalence rate and effects all age group equally.ii) Haloendemic --> A high level of infection begining early in life and affecting most of the child population, leading to a state of equilibrium such that adult population shows evidence of disease much less commonly than to the children, as in case of malaria">