The closest I could search on about
RX is that it is an SUV crossover
equivalent of Harrier.

What does the "RX" stand for?

RX- Recreational 4x4

Recreation Xtraordinair!

Highlander "R" X Crossover...dunno

Prescribes you to drop and give me 350!!

Reactor 350 comes close.

Rated Xtreme 350...

Lexus Acronyms keep me guessing.

Brochure isn't much help to define either.
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Here: RX: midsize crossover SUV
"RX" = Japanese inspiration
"the name has no specific meaning and simply denotes a luxurious and technological image."
- http://www.cars-directory.net/history/lexus/

RX came before Highlander and all were/are not 4x4.

My favorite is Recreational (X)cross-over.

Salim

The "X" was first used on the LX 450 which had a "full-time four-wheel-drive system." Thus, my post. However, would like to update that comment.

Technically, the "X" refers to all luxury utility vehicles from Lexus which includes crossovers and body-on-frame SUVs of all sizes and no matter if FWD, 4x4, AWD, etc.