The three building blocks of digital building delivery are BIM, VDC and Digital Twins. There are various definitions for these three things, but based on my experience I define them as follows:
- Building Information Modelling: a model with or without 3D geometry that hosts the information about building material, dimensions, connections, forces, power, flow rates, and all other elements required in each element that forms the building. 
- A key subset of understanding BIM is understanding Level of Development, or LOD. This means how realistic the building element is within your model. 
- Virtual Design and Construction: Before you can have VDC, you need to have BIM. With that model, you can now analyze for constructability and derive insight into how to optimize your construction process. This is where tasks like Clash Detection and 4D Scheduling come in.
- Digital Twin: a digital representation of your complete as-built conditions, including equipment tagging, maintenance and replacement lifecycles, and connections to the various IoT devices in your building that indicate how it is performing.

The key is to understand that having one of these items does not mean you have the other. If your BIM hasn’t been updated to record every condition of the building since it was constructed, it’s not a Digital Twin. And, in fact, Digital Twins can be created without the need for model authoring software like Revit or ArchiCAD. Despite what marketing materials tell you, a Digital Twin isn't a “bonus” outcome from BIM. It should, in fact, be the driving force behind how you author BIM and what VDC processes you use.