Electronとは

Electron は、JavaScript、HTML、CSS によるデスクトップアプリケーションを構築するフレームワークです。 Electron は Chromium と Node.js をバイナリに組み込むことで、単一の JavaScript コードベースを維持しつつ、ネイテイブ開発経験無しでも Windows、macOS、Linux で動作するクロスプラットフォームアプリを作成できます。
引用：　https://www.electronjs.org/ja/docs/latest

Electronに必要なFile

A basic Electron application needs just these files:

• package.json - Points to the app's main file and lists its details and dependencies.
• main.js - Starts the app and creates a browser window to render HTML. This is the app's main process.
• index.html - A web page to render. This is the app's renderer process.

引用：https://github.com/electron/electron-quick-start/blob/master/README.md

(render: to make an image on a computer screen appear solid and like a real object)← the basic meaning is "to cause something or someone to be in a particular state" or "to provide or give something such as help or a service to people".
引用：https://dictionary.cambridge.org/ja/dictionary/english/render