"Schmear" is a word of Yiddish origin, which is the historic name of cream cheese

Cream cheese

Cream cheese is a soft, mild-tasting, white cheese with a high fat content. Traditionally, it is made from unskimmed milk enriched with additional cream....

 spread upon a bagel

Bagel

A bagel is a bread product, traditionally shaped by hand into the form of a ring from yeasted wheat dough, roughly hand-sized, which is first boiled for a short time in water and then baked. The result is a dense, chewy, doughy interior with a browned and sometimes crisp exterior...

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Originally, the usage of the word schmear, or shmear, referred to a spread of cream cheese on a bagel. In modern usage it has extended to anything that can be spread, and in some cases refers to "an entire set or group of related things", or the expression "the whole shmear".

Sources

• http://query.nytimes.com/gst/fullpage.html?res=9501E1D9163AF934A15754C0A961958260
• http://www.highbeam.com/doc/1G1-151530407.html
• http://www.forward.com/articles/now-shmear-this/
• http://www.nydailynews.com/archives/entertainment/1997/06/08/1997-06-08_oy_vey_es_schmear__something.html