Password
The secret you use to prove you're you — still today's dominant authentication despite many attempts to retire it.
Good practice in 2026: at least 12 characters, unique per service, stored in a password manager (1Password, Bitwarden, KeePass). Passphrases ("sunflower-plays-accordion-on-mars") are better than complex short passwords.
On the server, passwords are never stored as text — always as a hash with bcrypt, argon2 or scrypt plus a unique salt per user.