The point of contact.

	// Print how many points are colliding this transform 
	// And print the first point that is colliding.
	function OnCollisionEnter(other : Collision) {
		print("Points colliding: " + other.contacts.Length);
		print("First point that collided: " + other.contacts[0].point);
	}

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    void OnCollisionEnter(Collision other) {
        print("Points colliding: " + other.contacts.Length);
        print("First point that collided: " + other.contacts[0].point);
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	def OnCollisionEnter(other as Collision) as void:
		print(('Points colliding: ' + other.contacts.Length))
		print(('First point that collided: ' + other.contacts[0].point))