what is this

in post man i put this json of mautic
“contacts”: {
“116641”: {
“isPublished”: true,
“dateAdded”: “2018-02-02T01:00:35+02:00”,
“dateModified”: “2018-12-04T11:48:48+02:00”,
etc. etc.

what is this anybody knows ?:
“116641”: <=========================