Abstract class and Interface

The abstract class can have abstract and non abstract class methods. But the interface should have all the methods in abstract format.

The abstract class can have access modifiers (internal and public). The interface will have the public as default access modifier.

The interface cannot have implementation of methods. But the abstract class can have non abstract methods.

The interface can be base class to implement the multiple inheritance. But the abstract classes cannot be base class to implement the multiple inheritance

You can see the difference in table format.

Features Interfaces abstract class

Multiple inheritance	A class may inherit several interfaces.	A class may inherit only one abstract class.
Default implementation	An interface cannot provide any code, just the signature.	An abstract class can provide complete, default code and/or just the details that have to be overridden.
Access Modfiers	An interface cannot have access modifiers for the subs, functions, properties etc everything is assumed as public	An abstract class can contain access modifiers for the subs, functions, properties
Core VS Peripheral	Interfaces are used to define the peripheral abilities of a class. In other words both Human and Vehicle can inherit from a IMovable interface.	An abstract class defines the core identity of a class and there it is used for objects of the same type.
Homogeneity	If various implementations only share method signatures then it is better to use Interfaces.	If various implementations are of the same kind and use common behaviour or status then abstract class is better to use.
Speed	Requires more time to find the actual method in the corresponding classes.	Fast