I didn't know what they were either, but saw a few quilts at the store using these and asked why were they made up like that, and the reply was that sometimes they were the same price as yard goods, but just smaller.
In Canada here only Walmart has them at lower than $8.00 for 4 in the quarter.
Sure would love to see a Joann's in my travel to the US next year.
I bought some and will be incorporating them in my next bright quilt.
http://quiltingforfunandmorefun.blogspot.com