Blazor is an open-source web framework that lets one build interactive web UIs using C# instead of JavaScript. Their apps are composed of reusable web UI components implemented using C#, HTML, and CSS. Moreover, both client and server code is written in C#, allowing one to share code and libraries.

Blazor is a feature of ASP.NET, the popular web development framework that extends the .NET developer platform with tools and libraries for building web apps.