As the hover-over mostly indicates, that’s Data (KV) service connections. I don’t recall the limit, but it’s in the 10s of thousands and scales well.
That said, if you see this number always growing, it may mean you’re leaking connections/objects somewhere. It’d usually stabilize somewhere around the number of client processes accessing the cluster in the typical environment. This, of course, varies based on deployment platform. 8000 sounds a bit high for small deployments.
I know you’ve posted about PHP before. If this is a PHP deployment, keep in mind there is one connection per process so you’ll not want to run tens of thousands of processes in most cases. There are some other options if required, but it’s a bit of an anti-pattern to, for instance, set Apache servers to 5000 per app server node.