Most wallets use the BIP39 standard for generating your wallet backups. Even altcoin wallets use BIP39 seed phrases. With this phrase you can restore all of your addresses and private keys in any wallet that is compatible with this standard.
but this is not native to btc core, correct? so if one uses a "seed phrase" for their keys, they always need some sort of software wallet to.....im not sure how to say it. make the seed phrase usable?
That's correct. The reference implementation of Bitcoin called "bitcoin core" doesn't support mnemonic algorithms so if you want to use your BIP39 mnemonic in it you'll have to derive the extended private key (xprv) from that seed phrase and then import that into core using "getdescriptorinfo" command with the desired derivation path.