There are many ways to make ruffles, but some of them are out of fashion now. Ruffles went through several hundred years of development and changing fashion, and sometimes went by different names, depending on the construction method and where they were attached to the garment.

The most common ruffle (today) is a long strip of fabric that is gathered along one long side. [Stephie][1] has already listed various ways how to create them. Pro tip: If you sew 2 gathering stitches in parralel and pull both of them, the ruffle will be neater and easier to attach to the straight fabric.

If you sew your gathering line in the middle of the strip of fabric, you end up with a **double ruffle** or **frill**.

[![enter image description here][2]][2]

A ruffle that is not gathered can be achieved by cutting a big circle, spiral or halfmoon shape from fabric and sewing the inner edge in a straight line to the piece of cloting. Since the inner circumference is smaller than the outer one, the fabric is longer on the outer edge and falls in waves. Thechnically this is called a **flounce** or **circular ruffle**.

[![difference between ruffles and flounces][3]][3]  
[Image source][4]

Historically, there were also pleated ruffles, but they are not very common anymore. [Knife pleated ruffles][5] can be made relatively easily on a sewing machine and there are even special sewing foots that automatically pleat the fabric while it's sewn. [Box pleated ruffles][6] are a little harder to make because (as far as I know) there's no way to automate the pleating (at least not for a hobby sewer). Often these are simply called **pleats**.

As with the gathered ruffle, you can move the gathering line to the center of the fabric to get **pleated frills**.

[![enter image description here][7]][7]
Knife pleated ruffle, [image source][5]

[![enter image description here][8]][8]
Box pleated ruffle, [image source][6]


  [1]: https://crafts.stackexchange.com/a/10117/6316
  [2]: https://i.sstatic.net/AirC4.jpg
  [3]: https://i.sstatic.net/DpPzs.jpg
  [4]: https://www.thecuttingclass.com/flounces-ruffles-circular-ruffles/
  [5]: http://bandycanyon.blogspot.com/2010/08/ruffle-tutorial.html
  [6]: https://www.onlinefabricstore.com/makersmill/how-to-make-pleated-and-gathered-ruffles/
  [7]: https://i.sstatic.net/Iv6G3.jpg
  [8]: https://i.sstatic.net/2uHMHm.jpg