What is a Holochain app?

I'm curious to know more about Holochain applications. Could you explain in brief what a Holochain app is? I understand it's a decentralized technology, but how does it differ from traditional blockchain-based apps? What are some of the key features or advantages of using Holochain for app development? Is it suitable for all types of applications, or are there specific use cases where it shines? I'd appreciate a concise yet informative answer to help me grasp the concept of a Holochain app.