"фигня" is a conversational word that is used to call anything that you don't know a proper name or nature of it. "Что это за фигня? -What is that thing?
It is also used to underline that something is not important. Don't worry, it's nothing. - "Не волнуйся, это фигня. "
Also, when somehing goes in an unexpected way, you can also call it "фигня" "Фигня какая-то"- Something is wrong.

What about "stuff/rubbish/pile of pants/bullshit/hogwash?

To Tatiana : I guess most of your words can be used. The only thing is that I can't think of a single word that could be used in all the situations.

I should say your explanation was rather detailed. Thank you for your comment!

I'm glad for the chance to help!