A relational database organizes data in structured tables, allowing for relationships through foreign keys. It employs SQL for data manipulation. In contrast, a non-relational database, often referred to as NoSQL, accommodates unstructured data and can include document, key-value, or graph formats. Non-relational databases excel in scalability and flexibility, making them suitable for big data applications where relationships are less critical. Each database type is optimal for different use cases, with relational databases excelling in transactional systems and non-relational databases in flexible, high-volume environments.