Symptomatic / asymptomatic
\sɪmptəˈmætɪk\ \eɪˌsɪmptəˈmætɪk\
Someone with a disease is said to be symptomatic if they exhibit symptoms of the disease. They are said to be asymptomatic if they do not.
When using the CFR to estimate the IFR of a disease, a major challenge is estimating the number of people that contracted the disease and were asymptomatic (or only mildly symptomatic).