CS8025 error

i have been using bits and pieces from burgzergarcade's hack and slash tutorials and i have recently done my modifiedStat script but there is an error (CS8025):

Assets/Ascripts/!Character/Charcter classes/ModifiedStat.cs(6,17): error CS0246: The type or namespace name `List' could not be found. Are you missing a using directive or an assembly reference? i copied nearly exactly

 using System;
 using System.Collections.Generic;
 
 public class ModifiedStat : BaseStat {
 
     private List _mods; //A list of Attributes that modify this stat
 
     private int _modValue; //The amount added to the baseValue from the modifiers
 
     public ModifiedStat() {
         _mods = new List<ModifyingAttribute>();
         _modValue = 0;
     }
 
     public void AddModifier( ModifyingAttribute mod) {
         _mods.Add(mod);
     }
 
     private void CalculateModValue() {
         _modValue = 0;
 
     if(_mods.Count > 0)
            foreach(ModifyingAttribute att in _mods)
              _modValue += (int)(att.attribute.AdjustedBaseValue * att.ratio);
     }
 
     public new int AdjustedBaseValue {
        get{ return BaseValue + BuffValue + _modValue; }
     }
 
     public void Update() {
         CalculateModValue();
     }
     
  
     public struct ModifyingAttribute { public Attribute attribute; public float ratio;
 
     public ModifyingAttribute(Attribute att, float rat) {
     attribute = att;
     ratio = rat;
     }
     }
 }

help please