another problem with bullets

I have problem with my bullets It don’t collision or something like that and It’s writing this ERROR
Tag: Bullet is not defined.
UnityEngine.StackTraceUtility:ExtractStackTrace ()
healthscript:OnCollisionEnter2D (UnityEngine.Collision2D)

HERE IS VIDEO OF THE PROBLEM : - YouTube

HERE IS THE CODE

public string bulletTag = "Bullet";
public HealthBar healthBar;
public int maxHealth = 100;
public int currentHealth;

 // Start is called before the first frame update
void Start()
{
    currentHealth = maxHealth;
    healthBar.SetMaxHealth(maxHealth);
}

void OnCollisionEnter2D(Collision2D collision)
{
    // Check if the object we collided with has the "Bullet" tag
    if (collision.gameObject.CompareTag(bulletTag))
    {
        TakeDamage(20);
    }
}

void TakeDamage(int damage)
{
    currentHealth -= damage;
    healthBar.SetHealth(currentHealth);
}

As the error message suggests, the tag used in your code is not defined. You can define it in the tags section of project settings. You will also need to assign the tag to your bullet object in the inspector.