Columnar Storage
In plain terms
Storing table data by column instead of by row.
Going deeper
Columnar storage keeps each column's values together, making analytical queries that scan few columns over many rows extremely fast. It also compresses well.
Under the hood
Great for OLAP aggregations and compression; poor for row-by-row transactional access.
Examples
Data warehouses, Parquet, Redshift, BigQuery, analytics, columnar DBs.
Think of it like...
Like filing all the 'ages' together and all the 'names' together, so totaling ages is instant.