I was asked the difference between a flounce and a ruffle so I thought I would see if I could explain and it is much easier to do using pictures but you must ignore my dislike of ironing :-).
This is a ruffle. You take a long strip of fabric and gather one edge before you attach it to your project. Here you can see the gathering at the sewn edge.
This is a flounce. It is harder to see without contrasting fabric but you will notice there is no gathering where the fabric is attached. To do this you do not use a long straight strip of fabric but a circular one.
This is the pattern I used for my flounce dress project for the flounces. The fullness of the lower edge of a flounce can be increased by making the inner circle smaller.
These are the main differences I think:
1. Flounces use no gathering so are faster with the sewing part.
2. Ruffles just requiring a strip of fabric and.are faster with the cutting out.
3. Flounces waste some fabric during cutting out because of their shape.
4. Flounces appear less bulky when being worn as there is no excess fabric close to the body.
Hope that helps :-)