What does Flannel mean?
Refers to any napped fabric whether it is twill, plain weave, printed, yarn dyed or solid color.
Heddels explains Flannel
Flannel is normally made out of wool and is a soft, loosely woven fabric known for its light weight and warmth. Used primarily for clothing, flannel is especially popular for shirts, pajamas, and sheets.
It became fashionable with the rise of grunge music in the early 1990s. Traditionally, flannel has a plaid pattern.
A snapshot of a men’s flannel shirt: