Whoa! That's a pretty bad curse in English. Be careful using it in a public forum like this. It is a combination of f***, which is an exceptionally bad word in English, and 'retard,' which is an old and very offensive name for a person with intellectual disabilities. It is used as an insult to describe someone who is/has done something stupid. Even among swears, it is very low because it is a new word and a mixture of swears. It sounds extremely childish, and it makes the person using it seem very childish and stupid as well. I love profanity, and I use it all the time, but this word is intended to be funny because of the stupidity of its combination of words. I strongly encourage you to study English profanity before you use it, and then it will be much more rewarding to use the right swears at the right time! :)

It's an ignorant word, that ignorant people say in hopes of bullying individuals.

it must be the synonym of "mothefucker"

A piece of advice: you don't need to use every single word you see.

dayot538 below explains what the word means and where it comes from. I would suggest forgetting this word altogether. There is never a need to use it.