Blockchain as a Service is a cloud-based service that enables users to build, host, and use their own blockchain apps, functions, and smart contracts without the need to maintain and setup the underlying infrastructure themselves. It's similar to how software as a service (SaaS) works, offering blockchain technology on a subscription basis, making it easier and more accessible for businesses, financial institutions and developers to leverage blockchain technology for various features like scaling up the blockchain solutions, secure transactions, and decentralization, without the complexity and cost of developing and managing a blockchain infrastructure on their own.