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1.
from Yiddish, shmalts, meaning rendered (melted) animal fat; usually chicken fat. Schmaltz is used to make matzo balls.

figuratively: a work of art that is excessively sentimental, sappy or cheesy.
That old Jewish guy at the next table is spreading schmaltz on his bread. It's so grody!

Gone With the Wind?! Why would you want to see that piece of 1930's schmaltz? Let's rent AVP instead!

by pogo747 September 19, 2006
 
2.
Any unidentified, nasty, liquid-like substance; usually very questionable in what the hell it actually is...
Be careful with this container Bill; it's full of some weird schmaltz...
by Testies321 August 12, 2010
 
3.
to take the last of something and not throw away the box or container that it came in, usually causing much anger in the next person to examine the aforementioned box.
Hey I'm gonna get a donut... What the hell, someone schmaltzed the last creme-filled!
by WuBuRZ October 27, 2011