Software performance is very important, early 2015 HTTP/2 came along that facilitated how Web Browsers request files from the Server. Http/2 is a complete revision of its predecessor HTTP/1.1 and offers more insights on delivering expected content through the protocol. According to Google Developers’ Web page, Http/2 help to reduce latency by allowing full request and response in a few transactions (Introduction to HTTP/2
| Web Fundamentals | Google Developers).
What this means is when a user requests a page to your Server, if a user is using the latest Google Chrome or Microsoft Edge Web Browser fully equipped with Http/2 capabilities then the Web Server would respond with the additional web page resources provided the Server knows most users navigate utilizes the resource related to the page you requested.
Basically, the Server makes the prediction about what resources an end user would need or what the next navigation would likely be and sends those resources through the wire before an end user actually makes a request.