A random speed along X, Y, and Z that is added to the velocity.

	// Spread random velocity mainly along x-z axis
	particleEmitter.rndVelocity = Vector3(2, 0.1, 2);

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    void Example() {
        particleEmitter.rndVelocity = new Vector3(2, 0.1F, 2);
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	def Example() as void:
		particleEmitter.rndVelocity = Vector3(2, 0.1F, 2)