I'd say that's a slab, but it's not a single slab with a center cutout (there are seams on 3/4 corners). This can actually be a very cost effective way of doing things, as almost all stone shops will have pre cut pieces from previous jobs called remnants, which are considerable cheaper than a fresh cutting of a stone. The downside of using these is that it will inherently have seams between the pieces. These can be a great way to achieve the look pictured, and it's what I feel was actually done in the picture.

Conversely, if you visit a smaller stone shop, they will likely have much smaller remnants and you may need to have a slab cut for your job.

There's a great video from marble.com's channel about remnants that can give you some of the in's and out's.

https://youtu.be/9mQrhhrr1y0

Hello, I always recommend using a slab - either a single piece or a 4-piece installation as pictured above. It's a much cleaner and more elegant look when working with marble.