Glossary
ECDSA
Elliptic Curve Digital Signature Algorithm — the signature scheme Bitcoin and Ethereum use to authorize transactions, parameterized over secp256k1.
ECDSA — Elliptic Curve Digital Signature Algorithm — is the signature scheme Bitcoin and pre-Schnorr Ethereum use. It runs over the secp256k1 elliptic curve and produces 64-byte signatures from 32-byte private keys.
ECDSA is widely supported but quirky: signatures are malleable (multiple valid signatures exist for the same message and key), and the scheme does not natively support multi-signatures, which is part of why Bitcoin moved to Schnorr signatures with Taproot.