Notably:
"The terms are used interchangebly. There are 3 basic types of cotton flannel:
1) Flannel. This is a cotton woven that is brushed on one or both sides. It is usually $7-10/yd, often called quilter's flannel. Since it's printed on finer cotton wovens before napping, prints can be more detailed. Used in shirts, expensive sleepwear and quilts. The face feels sueded, bach may or may not be napped..
2) Yarn Dyed Flannel. Made with flannelled (fuzzy) multi-colored yarns - always plaids or ginghams. Usually has a lower fuzz-factor than flanellette making it more suitable for shirts, lounge pants, sheets and jacket linings. Available in soft (for sheets and shirts) and tough weaves (for lumberjacks and horse tack).
3) Flanelette (of Flette in the trade). Woven with flannelled yarns. This is the low end soft and fuzzy flannel, $2-4/yd. Used for PJs, pillow cases, rag quilts, diapers, and sheets."