In Salesforce user can generate following report types:
Matrix Reports: The reports in which data can be grouped as either row or column wise are called Matrix reports.
Tabular Reports: The reports that are of Excel type and provides an item list along with a grand total are known as Tabular reports.
Joined Reports: When data of reports are fetched and shown by different reports that may be similar or different, then it is called Joined Reports.
Summary Reports: These reports are quite similar to Tabular reports, but you can also perform grouping of rows, you can create the charts, and view the subtotal as well.
Here, you can only use Summary and Matrix reports as the data source for dashboards, while joined and Tabular reports cannot be used.