applicationPackaging created the topic: what is MSI Script and its Installation Modes?
MSI Script contains 3 installation modes:

1. Normal Installation:
Select this installation mode to edit the sequences that are run during a normal installation. This is the most common type of installation.

If the application is not already installed when an end user double-clicks the installation .MSI, the standard installation wizard appears (Install Dialogs), which installs the product. If the application is already installed when an end user double-clicks the installation .MSI or if the end user selects it from the Add/Remove control panel, the installation runs in maintenance mode (Maintenance Dialogs), which provides options to modify, repair, or uninstall an application.

2. Administrative Installation:
Select this installation mode to edit the sequences that are run during an administrative installation.
An administrative installation copies a source image of the application to a network; the source image resembles the directory structure of the installed application. End users who have access to the administrative installation can then install the application from the network location.
To run an administrative installation, use the command line option /a. (Example: msiexec /a “C:\path\Sample.msi”.) An administrative installation uses the Admin Dialogs.

3. Advertisement Installation
Select this installation mode to edit the sequences that are run during an advertisement