A dynamic map layer refers to a layer in the current map service. More information on this can be found in the ArcGIS REST API help.
Referenced by: source
Properties
| Property | Details | 
|---|---|
| gdbVersion | If applicable, specify this to use an alternate geodatabase version. | 
| mapLayerId | The current map layer's id. | 
| type | A string value indicating the type. Valid value of this property mapLayer | 
dynamicMapLayer Example
{
  "type": "mapLayer",
  "mapLayerId": 3,
  "gdbVersion": "SDE.dynamicLayers"
}