Pixel tracking is the most commonly used mechanism to track the conversions. Similar to other pixels, Facebook tracking script (also called pixel) is put on every website page which you want to track. To track the conversions, pixels are placed on the post check-out page of your website.
A facebook tracking pixel is an HTML code snippet which is loaded when a user visits a website. It is useful for tracking user behavior and conversions. With a tracking pixel, advertisers can acquire data for online marketing, web analysis or email marketing. If you are running a Shopify store you can painlessly integrate multiple facebook pixels through Shopify Facebook Pixel App.