false negative

noun2

1. •
   A result of a test that shows as absent something that is present.

   • While a false positive from a cancer screening test will unnecessarily frighten a healthy person, a false negative will deprive them of timely treatment.
2. •
   A type II error (“accepting the null hypothesis when it is false”).

   • Statisticians sometimes refer to false negative results as Type II errors. Type II errors cannot be controlled explicitly, but are controlled implicitly via the experimental design. — 2003