An installation package (.msi file) contains all of the information that the Windows® Installer requires to install or uninstall an application or product and to run the setup user interface. Each installation package includes an .msi file, containing an installation relational database, a summary information stream, and data streams for various parts of the installation. The .msi file can also contain one or more transforms, internal source files, and external source files or cabinet files required by the installation.

Because the database is relational, changes made to one table are propagated automatically throughout the database. This is a very efficient process for introducing consistent changes into the installation process that simplifies customizing a large application or group of applications.  

Quick Tip: How to run installer file (.msi) from a command line?

msiexec /i “PackageName.msi”