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I have been trying to learn more about the SIR model since hearing about it due to recent events. In the process, I have heard various contradictory things. So I am seeking clarity. Specifically, I want to make sure I understand the R in SIR correctly. Does R stand for removed (ie, recovered or dead) or recovered?

It is my understanding that S is for susceptible (percentage of living population not yet infected) and I is for infected (percentage of contagious population).

Because the simplest SIR model implicitly assumes a recovered individual cannot transmit the virus (ie, immunity), I am inclined to think R has to be for removed to ensure that S+I+R=1; since the simplest SIR model does not account for population changes due to variable birth/death rates, I'm not sure that this equality relation holds. It follows that dS/dt + dI/dt + dR/dt = 0 ==> dR/dt = - (dS/dt + dI/dt), which makes me wonder: what is the model actually capturing regarding R?

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On regards of your question:

S: Susceptible (= N-confirmed cases)

I: Infected (= confirmed -recovered -deaths)

R: Recovered / fatal (= recovered -deaths)

For further reading: https://scipython.com/book/chapter-8-scipy/additional-examples/the-sir-epidemic-model/

Enjoy!

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