It comes from CCVault. I saw it in the 'Receive' tab.
You can specify a part of the address, or a derivation path like "m/1852'/1815'/0'/1/32", "1815 0 1 32" or "0 1 32".
...and what do the various numbers mean?
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Cardano follows the BIP32-ed25519 standard for HD key derivation. Read more about it here.
In a nutshell, a virtually infinite number of public/private addresses/keys pairs can be derived from a single master key-pair, which itself is derived from an entropic secret (usually in the form of a 24-word mnemonic). Staking (and all other types of) keypairs on Cardano can, in principle, be generated from the same set of root keys, though this is not recommended unless you know how to manage private keys yourself.
Keys used in Cardano transactions are 5 derivations away from the master seed. Your "wallet" is the middle number
x in that whole mess there.
m / 1852' / 1815' / x' / 0, 1, or 2 / n
' symbol means hardened derivation is used, meaning the child keypairs will be able to make keypaths of their own. if hardened derivation is not useed, the child keys will be "infertile".
Many unique wallets with unique staking keys can be derived from the same master seeds. Unfortunately, most wallet software like Daedalus and or Yoroi don't do this by default. The good news is this can all be done manually using CLI tools!