Dash is a python framework used for interactive web applications, without the need for HTML, CSS and JS.
Callbacks are used for interactivity in dash applications. You can define functions to set up activities that will happen once the app is initiated, or when a button is clicked.
The dash app in here takes information from Yahoo Finance and shows infoamtion pertaining to whichever ticker you input. You can also input multiple tickers at once on the Summary page.