What are the four types of Salesforce reports?

1. Tabular: Simple flat list of records with no subtotals. Good for exporting data. Cannot be used as a dashboard source.
2. Summary: Records grouped by one or more fields with subtotals per group. The most common report type. Can be used in dashboards.
3. Matrix: Rows and columns grouped simultaneously with totals at each intersection. Ideal for pivot-table style comparisons (e.g., revenue by product by region).
4. Joined: Multiple report blocks, each with different objects or filters, displayed side by side in one report. Useful for combining related but distinct data sets. Tabular, Summary, and Matrix share one data source; Joined can have up to five blocks from different report types.