also: たべカス
noun
leftovers; food scraps; leavings of a meal
Refers to uneaten food remaining after a meal, such as scraps on a plate or leftovers to be thrown away. Not used for intentionally saved leftovers (which is 残り物).
食器の上の食べかすを片付ける。
I clean up the food scraps on the dishes.
テーブルに食べかすが散らかっている。
There are food scraps scattered on the table.
noun
bits of food; food particles (in teeth/mouth)
Specifically refers to small food particles stuck in teeth or lingering in the mouth after eating.
歯の間に食べかすが詰まった。
A bit of food got stuck between my teeth.
口の中の食べかすをゆすぐ。
I rinse the food particles out of my mouth.
Compound of 食べ (stem of 食べる 'to eat') and かす ('scraps, dregs'). The かす part is of uncertain origin, but the word transparently means 'eating scraps'.