A noun meaning something that has been started but not finished; 'half-done' or 'in the middle of' (often used as 'やりかけの〜').
やりかけの仕事があるから、今日は早めに帰れない。
I can't leave early today because I have work that's still in progress.
彼はやりかけの本を机の上に置いたまま外出した。
He left the book he was reading unfinished on the desk and went out.
料理はやりかけで冷蔵庫に入れないで、早く仕上げてください。
Don't put half-prepared food in the fridge — finish it quickly, please.