a brand name for a system developed by the Apple company that allows users to store passwords, credit card numbers, and other important information safely on their computer, phone, etc.

Keychain is a type of password management system. “钥匙串”是密码管理系统的一种。

iCloud Keychain stores credit card numbers and expiry dates, passwords and usernames, Wi-Fi networks, Internet accounts, and more. iCloud 钥匙串可以存储信用卡号码和有效期、密码和用户名、Wi-Fi网络、互联网账户等等许多信息。

the Keychain system used by a particular person

To lock your Keychain, click the lock icon at the upper left-hand corner of the window. 如需锁定钥匙串，请单击窗口左上角的锁定图标。

Either create a new login keychain or update it with your new password. 要么创建一个新的登录钥匙串，要么用新密码更新。