utlbstat/utlestat... dc_used_extents

The following are just a few of the many options/features found in the REPORT.TXT file after running the utlestat. Where can I find out more about dc_user_extents and other dc_% values? Most of the typical 'cache buffers..' , 'library cache...' ... etc.. were covered in the Performance Tuning Workshop. But when I get high values for dc_% how do I diagnose these areas?

Thanks!

cache buffers chai
latch wait list
library cache
messages
modify parameter v
parallel query sta
process allocation
shared pool

dc_used_extents
dc_constraints
dc_histogram_de