Why does Bitcoin Core mention "Coinbase transactions", and what are they?

Quote:

"category" : "str",                  (string) The transaction category.
                                           "send"                  Transactions sent.
                                           "receive"               Non-coinbase transactions received.
                                           "generate"              Coinbase transactions received with more than 100 confirmations.
                                           "immature"              Coinbase transactions received with 100 or fewer confirmations.
                                           "orphan"                Orphaned coinbase transactions received.

Source: https://bitcoincore.org/en/doc/0.20.0/rpc/wallet/listsinceblock/

I get "send" and "receive", but what are "generate", "immature" and "orphan"? And why is Coinbase (the exchange?!) mentioned several times in core (no pun intended) Bitcoin Core functionality?!

Once again, there’s nothing but cryptic, very short "descriptions" of this, leaving me (and supposedly many others) guessing wildly.