What is a relational database?

a$.$

A collection of data, usually structured, organized as a set of tables with columns and rows.

b$.$

A collection of data, usually unstructured, with the flexibility to store and retrieve nontabular data.

c$.$

A type of database that is offered by major vendors including MongoDB, Amazon DynamoDB, and Apache Cassandra.

d$.$

A database that can be scaled easily with speed.