what does a redundant descending colon actually mean?!

You can probably get a better answer from your doctor, but...
It means you have a little extra curve in your descending (on the left side) colon.
One variation on the normal anatomy of the colon occurs when extra loops form, resulting in a longer than normal organ. This condition is referred to as redundant colon. It typically has no direct major health consequences.
A significant indirect health consequence is that use of a standard adult colonoscope is difficult and in some cases impossible when a redundant colon is present, though specialized variants on the instrument (including the pediatric variant) are useful in overcoming this problem.

If you aren't having problems/pain there is not much to worry about. However, next time you try to get a colonoscopy you will want to let them know what to expect.