While you are using the product, the rest of the product is being downloaded in the background. But with the streaming capabilities in Click-to-Run, you can open and start to use the product before the whole product is installed. If you install Office by using MSI, you have to wait until the whole Office product is installed before you can open and start to use the product. Click-to-Run is an alternative to the traditional Windows Installer-based (MSI) method of installing and updating Office.The streaming technology enables you to download and begin to use an Office product before the whole product is installed on your computer. Click-to-Run is a Microsoft streaming and virtualization technology that reduces the time that is required to install Office and helps you run multiple versions of Office on the same computer.
For detailed explanation follow the link Overview of Click-to-Run. I’ll give you the basic idea of what exactly is Microsoft office Click-to-Run.
