What type of search can be saved as a report?

Only searches that generate statistics or visualizations can be saved as a report. These are searches that contain a transforming command, such as stats, chart, timechart, top, rare, etc. Transforming commands create a data table from the events and enable various types of visualizations. Searches that do not contain a transforming command can only be saved as an alert or a dashboard panel. References: Splunk Core User Certification Exam Study Guide, page 35.