What is Blazor?

Blazor is a Single Page Application development framework. The name Blazor is a bastardisation 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 client side
Blazor app with client-side execution

Blazor also supports executing SPAs on the server. See Server-side components.