Blazor is a Single Page Application development framework. The name Blazor is a combination/mutation of the words Browser and Razor (the .NET HTML view generating engine). The implication being that instead of having to execute Razor views on the server in order to present HTML to the browser, Blazor is capable of executing these views on the client.
Blazor is not like Silverlight, Microsoft’s previous attempt at hosting in-browser applications. Silverlight required a browser plugin in order to run on the client, which prevented it from running on iOS devices.