A columnar database is a type of database management system that stores data in columns rather than rows. This structure allows for efficient data retrieval and analysis, especially for queries that involve aggregating large amounts of data. By organizing data in columns, it reduces the amount of data read from disk, which can significantly speed up query performance. Columnar databases are particularly useful for analytical workloads, such as those found in business intelligence and data warehousing. They are designed to handle large volumes of data and can efficiently process complex queries, making them popular choices for organizations that rely on data analytics tools like SQL and Apache Spark.