what is a script component??

i get a message when I try to add the script to my player saying: Cant add script to component 'Player' Because the script class cant be found...

This is my script:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class playermovement : MonoBehaviour
 {
     private Rigidbody2D myRidgidBody;
 
     [SerializeField]
     private float Speed;
 
     // Use this for initialization
     void Start ()
     {
         myRidgidBody = GetComponent<Rigidbody2D>();   
     }
     
     // Update is called once per frame
     void fixedUpdate ()
     {
         float horizontal = Input.GetAxis("horizontal");
 
         HandleMovement(horizontal);
     }
 
     private void HandleMovement(float horizontal)
     {
 
         myRidgidBody.velocity = new Vector2(horizontal * Speed, myRidgidBody.velocity.y);
     }
 }

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