Radiant Crossover is what RX represents but it's not clear what RZ mean, but it's safe to say the R likely means Radiant. What do you think the Z is for?
Lexus RX/RX L
The Radiant Crossover, or the Lexus RX, represents the automaker's envisioned future when it was launched at the start of the new millennium. The L suffix is used to denote the larger, seven-seater versions.