What is the difference between an Interface and an Abstract Class?

interface IVehicle
{ void GetFuelLimit();    void CalculateMileage(); }

Class Car:IVehicle
{
private void GetFuelLimit()
{
//some code
} 
private void CalculateMileage()
{
//some code
}  
}


Abstract Class:

abstract class Vehicle
{ 
private void GetFuelLimit()
{
//some thing
} 
void CalculateMileage(); }


Class Car:Vehicle
{

private void CalculateMileage()
{
//some code
}