Generic : Same property but different (compatible) types.

public abstract class Base
{
    public abstract void Use();
    public abstract object GetProp();
}
public abstract class GenericBase<T> : Base
{
    public T Prop { get; set; }

    public override object GetProp()
    {
        return Prop;
    }
}
public class StrBase : GenericBase<string>
{
    public override void Use()
    {
        Console.WriteLine("Using string: {0}", Prop);
    }
}
public class IntBase : GenericBase<int>
{
    public override void Use()
    {
        Console.WriteLine("Using int: {0}", Prop);
    }
}