MSI and CTR are both install methods for Microsoft Office.
MSI is “Microsoft Installer.” It is an installer file that has the full product in it. So it is a large file and most commonly used when installing from a DVD, but with high bandwidth internet, it has become more common to download the large installer file and then install the software.
CTR is “Click to Run.” It is a streaming installer that downloads the installation files during the install process. One of the key traits is the core application is installed, and can be used, while the additional features continue to install in the background. In general, a high bandwidth internet connection is needed (or lots of time to wait for the installer to stream the data needed to install). The technology was introduced with Office 2010, but with poor results. Today, CTR is most commonly used when installing Office 2013 as part of an Office 365 subscription or Office 365 Home Premium subscription.
– Troy @ TLC