Matrix4x4.zero

Description

Returns a matrix with all elements set to zero (Read Only).

using UnityEngine;

public class ExampleScript : MonoBehaviour
{
    void Start()
    {
        // will print:
        // 0.00000 0.00000 0.00000 0.00000
        // 0.00000 0.00000 0.00000 0.00000
        // 0.00000 0.00000 0.00000 0.00000
        // 0.00000 0.00000 0.00000 0.00000
        var matrix = Matrix4x4.zero;
        Debug.Log(matrix);
    }
}

Additional resources: Matrix4x4.identity property.