There are 4 types of report formats in Salesforce:
1. Tabular Reports: 
This is the most basic report format. It just displays the row of records in a table with a grand total. While easy to set up they can’t be used to create groups of data or charts and also cannot be used in Dashboards. They are mainly used to generate a simple list or a list with a grand total.
 
2. Summary Reports:
 It is the most commonly used type of report. It allows grouping of rows of data, view subtotal, and create charts.
 
3. Matrix Report: 
It is the most complex report format. Matrix report summarizes information in a grid format. It allows records to be grouped by both columns and rows. It can also be used to generate dashboards. Charts can be added to this type of report.
 
4. Joined Reports: 
These types of reports let us create different views of data from multiple report types. The data is joined reports are organized in blocks. Each block acts as a subreport with its own fields, columns, sorting, and filtering. They are used to group and show data from multiple report types in different views.
 
When we save a report only the parameters of the report get saved. The data is always evaluated in real-time (when a report is run). The report can be run manually as well as it can be scheduled to run automatically based on the running user.
The data which is displayed in reports is based on the running user’s sharing and security settings. But when we schedule a report we have to select a running user based on whose security and sharing settings the report is generated.

Please mark as Best Answer if above information was helpful.

Thanks,