Create with Code tutorial not working. Error CS0246 What should the "Other" be defined as?

Hello, I've been having problems with my "Create with Code" tutorial not working. It appears in Lesson 3.3 Don't Just Stand There. There is a reference to the OnCollisionEnter method and it uses "other" but i believe it needs to be defined but I don't know what to set it to. Line 39 I also considered a namespace missing but what could that be?

error CS0246: The type or namespace name `_other_______' Could not be found.
Are you missing a using directive of assembly reference?

I am a Newbie but I wanna do things right so here is the code with the Code Tags
Please Help

Code (CSharp):

1.  
2. using System.Collections;
3. using System.Collections.Generic;
4. using UnityEngine;
5.  
6. public class PlayerController : MonoBehaviour
7. {
8.     private Rigidbody playerRb;
9.     private Animator playerAnim;
10.     public float jumpForce = 10;
11.     public float gravityModifier;
12.     public bool isOnGround = true;
13.     public bool gameOver = false;
14.  
15.     // Start is called before the first frame update
16.     void Start()
17.     {
18.         playerRb = GetComponent<Rigidbody>();
19.         playerAnim = GetComponent<Animator>();
20.         Physics.gravity *= gravityModifier;
21.     }
22.  
23.     // Update is called once per frame
24.     void Update()
25.     {
26.         if (Input.GetKeyDown(KeyCode.Space) && isOnGround)
27.         {
28.             playerRb.AddForce(Vector3.up * 10 * jumpForce, ForceMode.Impulse);
29.             isOnGround = false;
30.             playerAnim.SetTrigger("Jump_trig");
31.             {
32.  
33.             }
34.         }
35.     }
36.     // here is the first new reference to "other" this is where I am not sure how
37.     // to fix this since it appears that the reference is invalid how do I fix this?
38.         private void OnCollisionEnter(Collision collision other)
39.     {
40.             if (other.gameObject.CompareTag("Ground"))
41.         {
42.             isOnGround = true;
43.         }   else if (other.gameObject.CompareTag("Obstacle"))
44.         {
45.             Debug.Log("Game Over Woody");
46.             gameOver = true;
47.             playerAnim.SetBool("Death_b", true);
48.             playerAnim.SetInteger("DeathType_int", 1);
49.         }
50.     }
51. }
52.