A TecAdmin article explains the /etc/shadow file in Linux.
Understanding the "/etc/shadow" File in Linux
The `/etc/shadow` file in a Linux system stores password information for user accounts. It is a secure file that is readable only by the root user and is used to store the encrypted password for each user account, as well as other optional password-related information. The `/etc/shadow` file contains one line for each user account, with the fields being separated by a colon (:). The below screenshot shows the number of fields in an entry:
