What does $ref mean in Windchill OData REST API

When looking at the "swagger" for servlet/odata in /Windchill/netmarkets/html/wrs/odata-to-swagger.jsp?v=4&d=ProdMgmt we can see most of the time in parameters a difinition as:

{
 "in" : "body",
 "required" : true,
 "schema" : {
 "$ref" : "#/definitions/PTC.ProdMgmt.CheckInParts.Body"
 }
 }

 My guess is that this means the body parameter is required and has a schema according to $ref. My question is: Where can I find "#/definitions/PTC.ProdMgmt.CheckInParts.Body" so I can see the schema?