Signature files or definitions are an important part of how antivirus and antimalware software works. These files contain information about different viruses and malware, which is used by the software to detect, clean, and remove detected threats. If you haven’t updated these files, then your antivirus software isn’t nearly as effective.
In Windows Defender, these files are automatically updated as part of the Windows Update process. By clicking on the Update tab, you can see the last time antivirus and antispyware definitions were downloaded by your system. To manually update them, you can click the Update button.
