Matchbook cover that was never used for the purpose.
"Flat - a matchbook cover before bookmatches are attached and formed into a matchbook. Flats can have a striking surface and score lines for folds. If there is no evidence of it being formed into a matchbook nor having bookmatches attached it is considered a flat. The majority of phillumenists do not keep flats and consequently are considered to have little or no financial value." (definitions from the BML&BS site)
Corresponding Russian term Ασκλες