The term preload relates to techniques for improving performance by loading data/contents into memory/cache before processing or displaying it to users: preloading images in browsers to avoid delay in image rendering, preloading data from databases to RAM to avoid DB queries, and so on.
For preloading of Web resources, https://w3c.github.io/preload/ “defines the preload keyword that may be used with link elements. This keyword provides a declarative fetch primitive that initiates an early fetch and separates fetching from resource execution.”
Examples:
<link rel="preload" href="/styles/other.css" as="style">
<link rel="preload" href="/assets/font.woff2" as="font" type="font/woff2">
<link rel="preload" href="/style/other.css" as="style">
<link rel="preload" href="//example.com/resource" as="fetch" crossorigin>
<link rel="preload" href="https:…/x.woff2" as="font" crossorigin type="font/woff2">
<link rel="preload" href="app.js" as="script" onload="pDone()" onerror="plErr()">
