Relational databases provide a structured approach for storing and organizing large volumes of data into tables consisting of rows for records, and columns for attributes. They use primary keys which are unique identifiers for records and foreign keys, to establish well defined relationships between tables.
These databases are widely used since they are reliable, consistent, and highly adaptable to various applications. They also provide complex database queries and operations capabilities using a structured query language (SQL). They are backed up with a strong and mature ecosystem; with extensive tooling and community support.
MySQL, PostgreSQL, MariaDB, Microsoft SQL Server, and Oracle