식은 죽 먹기 (Sigeun juk meokgi)

Literally: Eating cold porridge

Example: “이 정도 문제는 식은 죽 먹기야.” — A problem like this is a piece of cake.

English equivalent: A piece of cake

Origin: Draws on the genuinely gentle, unchallenging nature of rice porridge (juk) as food: mild-tasting and smooth enough to be given even to sick patients who can't manage anything more solid, and easy to swallow without any real effort. Hot porridge carries one small risk — the danger of burning the roof of your mouth — but porridge that has cooled removes even that minor hazard, leaving genuinely nothing standing between you and finishing the bowl. The phrase belongs to a small family of similar Korean expressions built on equally effortless images, including "누워서 떡 먹기" (eating rice cake while lying down) and "땅 짚고 헤엄치기" (swimming while touching the ground) — all pointing at tasks so easy they barely count as tasks at all.