oon ▁doors , ▁also ▁known ▁as ▁ca fe ▁doors , ▁often ▁use ▁bid irection al ▁h ing es ▁that ▁close ▁the ▁door ▁regardless ▁of ▁which ▁direction ▁it ▁is ▁opened ▁by ▁incorpor ating ▁spr ings . ▁Sal oon ▁doors ▁that ▁only ▁extend ▁from ▁kne e - level ▁to ▁ch est - level ▁are ▁known ▁as ▁bat wing ▁doors . ▁ ▁A ▁blind ▁door , ▁Gib b ▁door , ▁or ▁j ib ▁door ▁has ▁no ▁visible ▁trim ▁or ▁oper able ▁components . ▁It ▁is ▁designed ▁to ▁bl end ▁with ▁the ▁adjacent ▁wall ▁in ▁all ▁finish es , ▁and ▁vis ually ▁to ▁be ▁a ▁part ▁of ▁the ▁wall , ▁a ▁dis gu ised ▁door . ▁ ▁A ▁French ▁door ▁consists ▁of ▁a ▁frame ▁around ▁one ▁or ▁more ▁transparent ▁or ▁transl uc ent ▁pan els ▁( called ▁lights ▁or ▁l ites ) ▁that ▁may ▁be ▁installed ▁sing ly , ▁in ▁matching ▁pairs , ▁or ▁even ▁as ▁series . ▁A ▁matching ▁pair ▁of ▁these ▁doors ▁is ▁called ▁a ▁French ▁window , ▁as ▁it ▁res emb les ▁a ▁door - height ▁cas ement ▁window . ▁When ▁a ▁pair ▁of ▁French ▁doors ▁is ▁used ▁as ▁a ▁French ▁window , ▁the ▁application ▁does ▁not ▁generally ▁include ▁a ▁central ▁m ull ion ▁( as ▁do ▁some ▁cas ement ▁window ▁pairs ), ▁thus ▁allowing ▁a ▁wider ▁un ob struct ed ▁opening . ▁The ▁frame ▁typically ▁requires ▁a ▁weather ▁strip ▁at ▁floor ▁level ▁and ▁where ▁the ▁doors ▁meet ▁to ▁prevent ▁water ▁ing ress . ▁An ▁esp ag no lette ▁b olt ▁may ▁allow ▁the