# What does the core stage of a launch vehicle mean?

I have seen the use of the term 'core stage' in the context of space launch vehicles. I am not able to clearly understand what it exactly means? I have learnt about launch vehicles having multiple stages: first, second and so on. Is the core stage just a different name for the first stage itself?

I tried to google it but couldn't get a clear meaning for it. I had a look at the SLS core stage fact sheet by NASA which says a few things about core stage.

• It says that the core stage stores cryogenic liquid hydrogen and liquid oxygen. So, this makes me think that this might not be the same as the first stage because you don't generally carry a higher $$I_{sp}$$ fuel like liquid hydrogen in the first stage (however, I may be completely wrong and maybe it is used in first stage here) and so this must stay at least till the stage which actually uses this cryogenic liquid hydrogen separates.
• It mentions that it houses the flight computers and much of the avionics needed to control rocket's flight. This again makes me think that the core stage is not same as first stage because the avionics and flight computers should be necessary for rocket after first stage separation too. Is it that the upper stages have their own flight computers and avionic system?

Thank you.