吃掉(chī diào) - to eat up, to finish off in Mandarin

吃掉 (chī diào) is 吃 with a result attached. 掉 on its own means to fall or to drop, but bolted onto a verb it means away or off, so 吃掉 is not just eating but eating something out of existence: eat it up, polish it off, finish the lot.

It turns up constantly with 把, because the sentence is usually about what happened to the food rather than about the eater: 他把蛋糕吃掉了. It also works figuratively, for costs and profits that swallow something whole.

The trap for English speakers is reaching for plain 吃 when you mean up. 我吃了蛋糕 says you ate cake; 我把蛋糕吃掉了 says there is no cake left. Mandarin puts that difference in the complement, not in a stressed particle at the end, so if you drop 掉 the finality simply disappears.