Liskov Substitution Principle

Without LSP:

Example, we are creating different robots, Kawasaki, Yaskawa, and ABBRobots all inheriting IRobots and have methods like Connect(), Operate() , Move(). Later say some new functionality in ABBRobots like ReportFaultData() is introduced, so we need to added ReportFaultData() in interface and other robots should do " throw NotSupportedException("Reporting fault data is not supported");" , this leads to compile time error or we need to do nothing, and so we need to change other classes.

With LPS:

Instead we will create new interface ISupportsFaultDataReporting and add the new ReportFaultData() and inherit only for ABBRobots 

public class ABBRobots : IRobots, ISupportsFaultDataReporting 
{
}

public class Program
{
    public static void Main()
    {
        List robots = new List{new Kawasaki(),new Yaskawa(),new ABBRobots()};
        foreach (var robot in robots)
        {
            robot.Move();
            if (robot is ISupportsFaultDataReporting faultDataReportingRobot)
            {
                faultDataReportingRobot.Report();
            }
        }
    }
}

Without LSP:

Why the name substitution - The idea is that you should be able to substitute the base class with the derived class without breaking the functionality.

 // Substituting base class with dereived class
        Shape shape = new Rectangle(5, 10);