C#: What is the difference between WeakReference and WeakReference<T>?

1// WeakReference
2var weak = new WeakReference(new object());
3if (weak.IsAlive)
4    var obj = weak.Target;
5
6// WeakReference<T>
7var weak = new WeakReference<StreamReader>(reader);
8if (weak.TryGetTarget(out var target))
9    target.ReadLine();