"and find out what the 'RT' in RTOS stand for"

It stands for 'Predictably Slow' as opposed to something like Windows which is 'Unpredictably Slow'.

'PSOS' is a bit of a mouthful though, so I guess they just made up the RT bit. 'Real Time' sounds exciting to the sort of people to whom it doesn't occur to ask "Hang on, what other kind of time is there anyway? Fake time? Einstime? (Sorry)"

I've talked to some otherwise really, really clever people who actually think that the only way to achieve a deterministic system is to use an RTOS. It doesn't seem to occur to them that you might not need any sort of TOSS at all.