It is actually way more complex than that. Nowadays it doesn't get explained a lot anymore. Especially with every system coming with some fancy bash or zsh with somewhat sane defaults.
But in the past you may have got just some naked Bourne Shell with no defaults at all.
UNIX Power Tools defined, and largely proved the sole occupant, of a class of technical literature.
It's the single book that more than any had me finally grok Unix. I still have my copy, first edition, two-colour printing (blue for "hyperlinks" to related sections).
Jerry Peek is also an absolute treasure for Unix shell wisdom --- bash in particular though he's highly knowledgeable about others as well.
But in the past you may have got just some naked Bourne Shell with no defaults at all.
https://docstore.mik.ua/orelly/unix3/upt/ch30_14.htm explains a bit.
They don't make books like this anymore. ;)