Can anyone explain what an offset is?

Hi. I am new with Unity and I am watching a tutorial, but I don't understand what the offset is. Can anyone please explain to me every step from this code?

using System.Collections; using System.Collections.Generic; using UnityEngine;

public class AnimatedTexture : MonoBehaviour {

 public Vector2 speed = Vector2.zero;

 private Vector2 offset = Vector2.zero;
 private Material material;

 // Use this for initialization
 void Start () {
     material = GetComponent<Renderer> ().material;
     offset = material.GetTextureOffset ("_MainTex"); 
 }
 
 // Update is called once per frame
 void Update () {
     offset += speed * Time.deltaTime;
     material.SetTextureOffset ("_MainTex", offset);
 }

}

Also I want to know what Set/GetTextureOffset(...) does. Thank you.