About
Language - (Main|Application Entry point) in a web application
App type
Web App
In a frontend web application, it's a file called the home page that creates an HTML page.
Library
In the context of a library (to bundle), the main file may be:
- a javascript file to create a javascript library
- a css file to create a bundled stylesheet
To know more, check the dedicated page: Web - Build Operations / Build Pipeline