Acronyms in aviation are a nightmare.
I've been in this game for 41 years and am amazed at the number that come up that I don't know or get confused by.
A few years ago, just for fun, we tried to do a flight without using acronyms.
So the VOR is "VHF Omni Range". Damn! "Very High Frequency Omni Range".
With acronyms whithin acronyms it soon became impossible.
The point is, when posting on here, don't assume that everybody understands your acronym.
Something in brackets as Simon 150 did with ICU can be a great help.
As for a Transformer Rectifier Unit:- It converts AC (Alternating current) into DC(Direct current) and normally reduces the Voltage from 115 to 28.
An Inverter will do the same thing in reverse.
Hope this helps.