Everybody understands the idea of space. You move forward, backward, left, right, up, down. Those are your three dimensions of space. Time is the fourth dimension, something continuously progressing. We move forward in time just by existing.

Now, imagine if you could combine these four dimensions. That's spacetime. In other words, you can think of spacetime like a loaf of bread where slices are moments of time. Each slice represents a snapshot of the universe at a particular moment.

The spacetime idea confounds our everyday understanding because we usually perceive space and time as separate. But when it comes to really big and fast things like planets and light, space and time start affecting each other.

One of the most fascinating things about spacetime is that it can be bent and stretched by massive objects like stars and planets. This curvature or dent from massive objects is what causes what we feel as gravity. Yes, that's right – when you drop a ball, it's not that some invisible force is pulling it towards the Earth, but rather that the Earth's mass is causing a curve in spacetime that the ball simply follows.

It's also worth mentioning that the faster an object moves, the slower time passes for it. This is known as time dilation - one of the weirdest outcomes of meshing space and time together.

In conclusion, spacetime is an integral part of our universe that combines our three familiar dimensions with the progression of time. It's a flexible entity that can be curved by mass, it links together all points in the universe, and it's at the heart of the modern understanding of gravity and even the nature of the universe itself. The concept may be abstract and challenging to visualize, but it is key to understanding our reality.