The Serializable attribute lets you embed a class with sub properties in the inspector.
You can use this to display variables in the inspector similar to how a Vector3 shows up in the inspector. The name and a triangle to expand its properties. To do this you need create a class that derives from System.Object and give it the Serializable attribute. In JavaScript the Serializable attribute is implicit and not necessary.
class Test extends System.Object {
var p = 5;
var c = Color.white;
}
var test = Test ();
using UnityEngine;
[System.Serializable]
class Test : System.Object
{
public int p = 5;
public Color c = Color.white;
}