There are multiple definitions:

1. half-value layer(English)

   • the thickness of an absorbing material required to reduce the intensity or exposure of a radiation beam to one half of the initial value when placed in the path of the beam
   • AGD, FID, ICRP, 2ABD
   • Radiotherapy /radiation
   • https://doi.org…1747-017-0026-1

2. high viral load(English)

   • LVL, CMV, EBV, HIV, IVL
   • Virology
   • https://doi.org….1002/jmv.24441