There are multiple definitions:

1. bromothymol blue(English)

2. poxvirus and zinc finger(English)

   • aka POZ
   • BTBD9, POZ

3. breakthrough bleeding(English)

   • Gynecology

4. bridge to bridge(English)

   • BTT
   • Cardiology, Transplantation
   • https://doi.org…acc.2020.04.037

5. bone-tendon-bone(English)

   • refers to a patellar graft. Also denoted as B-T-B
   • ACL
   • Skeleton and bone (formation), Knee, Surgery
   • https://doi.org…ats.2021.08.002

6. blood-testis barrier(English)

   • CSF, SSV
   • Embryology /reproduction, Genitals, Andrology
   • https://doi.org…3/molehr/gax017

7. bric-a-brac, tram track, broad complex(English)

   • FLAG, GSH, GSSG, HA, HMWK, HRP, IAB, Keap1, luc, mRNA, Neh2, NEM, NO, NQO1, Nrf2, PDB, ROS, SN2, tBHQ, Tg, UGT1A1, WT, ARE, CLR, CUL3, DTNB, EPA
   • https://doi.org…9/ars.2010.3273