There are multiple definitions:

1. phytase unit(English)

   • ADF, ATTD, NDF, SBM, STTD
   • Nutrition, Veterinary medicine
   • https://doi.org…1093/jas/sky152

2. functional tissue unit(English)

   • T, AG, CAD-RADS, DSC, EAT, FAI, FCN, IoU, IRP, MIS, ORFAN, PCAT
   • Medical imaging, Signal analysis, Artificial intelligence, Coronary circulation
   • https://doi.org…SS.2020.3008190