What is the "application / ld + json" type used in a script tag?

I was looking at the source code of the Kickass page and this passage caught my attention:

<script type="application/ld+json">
{
   "@context": "http://schema.org",
   "@type": "WebSite",
   "url": "https://kat.cr",
   "potentialAction": {
      "@type": "SearchAction",
      "target": "https://kat.cr/usearch/{q}/",
      "query-input": {
        "@type": "PropertyValueSpecification",
        "valueRequired": true,
        "valueName": "q"
      }
   }
}
</script>

Is this some definitions of some framework and / or library? What is the purpose of using type="application/ld+json" in a tag script? What can be done with this?