Initialism of tracheobronchial amyloidosis.
"The patient's rare respiratory condition was identified as TBA, or tracheobronchial amyloidosis, during the biopsy analysis."
In plain English: TBA stands for to be announced, meaning something will happen later but hasn't been decided yet.
"The event details are currently listed with tba on the flyer because nothing is confirmed yet."
Initialism of to be announced.
"The date and location for the conference are still tba."