Based on the structural differences, Salesforce has four different types of reports:
Tabular Report A tabular report displays data in the form of an Excel-like table that provides a list of items with the grand total.
Joined Report A joined report is a combined report having multiple blocks that show data from different reports, either of the same or of different report types.
Matrix Report A matrix report works for 2-dimensions and allows to group records row-wise and column-wise.
Summary Report In a summary report, the view is in a table form only, but it has more functionalities like grouping rows (only), viewing subtotals, and creating charts.