What is meant by to prettify JSON

I have heard of sites that prettify/beautify JSON. What does it actually mean?

This means a more human readable version of it. E.g. the following is valid json, but not well readable:

{"outcome" : "success", "result" : {"name" : "messaging-sockets", "default-interface" : "external", "include" : [], "socket-binding" : {"messaging" : {"name" : "messaging", "interface" : null, "port" : 5445, "fixed-port" : null, "multicast-address" : null, "multicast-port" : null}, "messaging-throughput" : {"name" : "messaging-throughput", "interface" : null, "port" : 5455, "fixed-port" : null, "multicast-address" : null, "multicast-port" : null}}}, "compensating-operation" : null}

After prettyfying this could look like this:

{
   "outcome":"success",
   "result":{
      "name":"messaging-sockets",
      "default-interface":"external",
      "include":[

      ],
      "socket-binding":{
         "messaging":{
            "name":"messaging",
            "interface":null,
            "port":5445,
            "fixed-port":null,
            "multicast-address":null,
            "multicast-port":null
         },
         "messaging-throughput":{
            "name":"messaging-throughput",
            "interface":null,
            "port":5455,
            "fixed-port":null,
            "multicast-address":null,
            "multicast-port":null
         }
      }
   },
   "compensating-operation":null
}