KeyCode.Mouse1

Description

Right mouse button (or secondary mouse button).

Use this to detect right mouse button presses. The “1” mouse button is the secondary button on the user’s mouse, which is usually the right mouse button. Unity defines this as the "1" mouse button, as the mouse button numbering begins at 0.

using UnityEngine;

public class Example : MonoBehaviour
{
    void Update()
    {
        //Detect if the right mouse button is pressed
        if (Input.GetKey(KeyCode.Mouse1))
        {
            Debug.Log("Mouse 1");
        }
    }
}