Scripting Reference
Vector3.operator -

static operator - (a : Vector3, b : Vector3) : Vector3

Description

Subtracts one vector from another.

Subtracts each component of b from a.

JavaScript 
    // prints (-5.0,-3.0,-1.0)
    print (Vector3(1,2,3) - Vector3(6,5,4));
using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Example() {
        print(new Vector3(1, 2, 3) - new Vector3(6, 5, 4));
    }
}
import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Example():
        print((Vector3(1, 2, 3) - Vector3(6, 5, 4)))

static operator - (a : Vector3) : Vector3

Description

Negates a vector.

Each component in the result is negated.

JavaScript 
    // prints (-1.0,-2.0,-3.0)
    print (-Vector3(1,2,3));
using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Example() {
        print(-new Vector3(1, 2, 3));
    }
}
import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Example():
        print(-Vector3(1, 2, 3))