Nostr is a decentralized media platform. What does that mean? It uses many distributed servers named "relays", and you choose which one you want to connect to. Your data is published in the relays, and other people can read it on these relays. You can have as many relays as you want, so in case one relay is out, your publications (in nostr is called "notes") will still be available on the others. The relays can be run by anyone, and you can also run your own. This relays configurations are what makes it almost uncensorable. While the server side of things is where the many users data is stored, to access and publish, you have to use software called "client". There are many clients avaliable, for many platforms, and with different features. Finally, the best part of nostr is how to react to content: Besides being able to "like" notes, it is also possible to send micro-payments in bitcoin with (almost) no taxes and no middleman. It is a direct connection between users and content creators. Ps.: You are going to love the memes there.