Domain name without top-level domain?

http://(7bbb41211116 or 127.0.0.1):8888/?token=7c33d3639a73a2d16213d24fd94f9406ee25526b5553b410

I noticed while running a docker image something that seems to look like a domain name, without a .TLD

I wasn't aware that this was possible. Can someone explain to me what are the requirements for doing this? I am interested in building a system that allows individuals to publish content on a domain of their own without a .TLD, it seems more open and user friendly than centralized web social networks. They could potentially communicate with each other in this manner, by allowing node to node communication using a separate protocol of my own design.

When I tried to use this label and connect to 7bbb41211116:8888, I received a "domain unreachable" error. Can someone help me understand what's going on?

Thank you.