What does "Ни пуха ни пера" Russian expression mean?

How do you wish good luck in Russian?

One of the most common wishes of good luck in Russian language sounds as: Ни пуха ни пера! 

It’s quite strange if you know Russian, because  пух means down, перо means feather.

Pay attention that this is not a simple way of wishing  success, you should use Ни пуха ни пера!  for example, before an exam, or before the job interview or any other special occasion where you need luck.

And you ( that person whom somebody wishes good luck) in reply you should say: К чёрту!  which  means «Go to hell!» 

Yes, yes, that’s not a mistake, you should reply in this particular way. 

As a matter of fact but this is the ancient Russian spell (I don’t know what is the best word for this occasion, the dictionary gives me a lot of examples: conjuration; incantation; abracadabra; adjuration; invocation, sorcery) 

I would call it «spell» now, ok?

The origin of this strange Russian  expression was found is in ancient times. The hunters in Russia ( probably in the other countries as well) were very superstitious.  They believed that demon spirits existed and they (demons) captured their success. 

According to the hunters language, перо signified a wild bird   and пух denotes a wild animal.

The hunters of those times were had a horror that somebody could wish them good luck, demons would hear and they could not catch a bag. As a consequent that was very important during those times without money and supermarkets. 

That’s why they everybody  was saying the spell  to the hunter "Ни пуха ни пера!"  and he always replied "К чёрту!"
  They believed the demons considered these words to be a quarrel or regrets of bad hunt.  Having heard these words demons thought that this hunter was unlucky and went away.

Examples: 

• Машины тронулись и медленно поплыли к воротам. «Ни пуха ни пера! Счастливого пути!» – слышалось из толпы. (Б. Полевой.)

• «Ни пуха ни пера!» – традиционной фразой пожелал мне успеха главный режиссер. (Н. Черкасов.)

• Все будет как надо… Ни пуха ни пера! (Ю. Бондарев.)

In English language you  can say: 

I'll keep my fingers crossed for you!

Knock on wood!

Touch wood!