Eating everything on one's plate or in a container; used as a noun or as the verb '完食する'. Common in restaurant reviews and everyday speech.
子どもがカレーを完食してくれてうれしかった。
I was happy that my child finished all the curry.
大食いチャレンジで最後まで完食できたら賞金が出る。
In an eating challenge, there's a prize if you can completely finish everything to the end.
『完食しました』と店員に言って、お皿を下げてもらった。
I told the waiter 'I've finished everything' and had the plate cleared.