In my Point of view 

Complex reports is 

I have created many reports using VB macro like 

I had created one control report which is defined many Sales
ares, Plants, Sales repcode..... like i have created control
reports and based these refer to created another report
which is refer to control report and run the each area or ,
sales repcode.... like that i have created and these reports
will be published individually on webi.

I thought that these type of reports are called Complex reports.

Thanks,

Complex reports are the reports which pull up data from 
different sources. Complexity also depends on the data 
model and the critical way the report data is going to be 
generated.