כֶּסֶף מְזֻיַּף (KEH-sef me-zoo-YAHF) is counterfeit money. לְזַיֵּף (le-zah-YEF) is to counterfeit. The root of both is ז.י.פ (z.y.p/f).
One can also counterfeit a decent voice while singing. In English we call this phenomenon singing off-key. In Hebrew, we call it לזייף - to sing off-key - or זִיּוּף (zee-YOOF) - the act of singing off key.
I write about this as I will be performing at the Open Mic Night hosted by AACI, Nefesh B'Nefesh and RustyMike Radio. Whether what I'll be doing is singing or מְזַיֵּף (me-zah-YEF) - singing off-key - is up to the crowd to decide.