TimePeriod is your date range and Spend is your cost. To find more human readable explanations of the columns, visit the ReportRequest Data object page (http://msdn.microsoft.com/en-us/library/bb671813.aspx), scroll down to the Remarks section, and drill down into the type of Report you want to request. Once inside the type of report you need, scroll down to the Elements area and click on the link under the Data Type column for the Columns row. Scrolling down into the Values section will give you the description for each column.
More specifically and for the KeywordPerformanceReport, you can access the descriptions for the report columns here:
http://msdn.microsoft.com/en-us/library/bb672087.aspx
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