Diff Between New and Override keyword in c#

Override: When a method of a base class is overridden in a derived class, the version in the derived class is used, even if the calling code didn't "know" that the object was an instance of the derived class.

New: If you use the new keyword instead of override, the method in the derived class doesn't override the method in the base class, it merely hides it.

public class BaseClass
{
    public virtual void AMethod()
    {
    }
}
 
public class DerivedClass : BaseClass
{
    public override void AMethod()
    {
    }
}
 
// ...
 
BaseClass baseClass = new DerivedClass();
baseClass.AMethod();

public class BaseClass
{
    public virtual void AMethod()
    {
    }
}
 
public class DerivedClass : BaseClass
{
    public new void AMethod()
    {
    }
}
 
// ...
 
BaseClass baseClass = new DerivedClass();
baseClass.AMethod();
 
DerivedClass derivedClass = new DerivedClass();
derivedClass.AMethod();