OLAP: Online Analytical Processing. Cranking through large amounts of data with a focus on aggregations like sums, averages, medians, etc. Measures (numbers) are defined by dimensions (attributes with usually discrete domains). Aggregations are frequently precomputed on many (or all) dimension axes so that they are immediately available. Models can be built from something as simple as a wide CSV file or as complicated as a snowflake schema.

The kind of relational database you're familiar with is probably OLTP (Online Transactional Processing).