An MSI-based install is a Windows software deployment that uses an .msi package, the classic Microsoft Installer format. In Office environments, it is one of the ways Microsoft Office can be installed and serviced, alongside other deployment models such as Click-to-Run.
For security teams, the install type matters because it changes how patches are delivered, tested, and rolled back. An update or compatibility issue may affect MSI-based Office builds differently from other builds, so administrators should confirm the exact deployment method before troubleshooting or making exceptions. Attackers also benefit from this diversity: defenders who assume every endpoint is patched the same way can miss exposure in a subset of machines. In practice, MSI-based installs are checked during patch triage, software inventory, and incident response to understand whether a problem is a vulnerability, a regression, or a configuration mismatch.