Relational databases are a type of database management system that organizes data into structured tables, consisting of rows and columns. Each table represents a different entity, and relationships between these tables are established through key columns. This structure allows for efficient data retrieval and manipulation using Structured Query Language (SQL). Relational databases are particularly well-suited for handling large volumes of structured data and complex queries, ensuring data integrity through ACID properties (Atomicity, Consistency, Isolation, Durability). They are widely used in various applications, from business operations to web development, due to their robustness and reliability.