Though it's a buzzword now, the idea behind 'digital twins' was that you not only have a detailed and faithful model (of an item, or process, or system, or network, etc.) whose granularity is congruent with the level of granularity that interests you about the real thing, but you also have bi-directional movement of data between the 'real' thing and its model.

So you can have sensor and measurement data from the real thing be streamed to the model in (ideally) real-time, you can make decisions off of the state of the model, and have those decisions be sent back out into the real world to make a change happen.

The specific wording of digital twins originated from a report discussing innovations in manufacturing, but I find that railway systems and operations make for some of the best examples to explain the concept, because they manage a diverse set of physical assets over which they have partial direct control, and apply conceptual processes on top of them.

Here's three assorted writings [1][2][3] that explain how railways would benefit from this.

[1] https://www.anylogic.com/digital-twin-of-rail-network-for-tr...

[2] https://www.railwayage.com/analytics/how-digital-twins-suppo...

[3] https://www.railwayage.com/analytics/realizing-the-potential...