Definition
In Korea, Sambok is the name for the three hottest days of the year, Chobok, Jungbok, and Malbok, counted together. They don't fall on fixed solar or lunar calendar dates. Instead, they are set by finding certain days marked with the character 'gyeong' (庚) in the traditional ten-stem cycle, counting from the summer solstice and the start of autumn.
The Day Autumn Lies Flat Under the Heat
Picture a stifling midsummer afternoon. You're crossing the street, and the heat rising off the asphalt makes you shrink into yourself. People in old Korea felt much the same way during the hottest stretch of the year.
In Sambok, the character 'bok' (伏) was drawn as a person lying low on the ground, like a dog. In the traditional cycle of seasons, the cool, metal-like energy of autumn is supposed to start pushing up around now. But summer's fire energy is so strong that autumn's energy doesn't dare stand up and lies flat on the ground instead.
People back then believed that heavy sweating drained your energy and left your insides cold. So they fought heat with hot food: dog meat soup, red bean porridge, or a rich chicken broth. Today many people go for samgyetang (Korean ginseng chicken soup) or grilled eel. It's the 'fight fire with fire' wisdom of a summer tradition, known in Korean as iyeolchiyeol.
Sambok Dates Aren't Lunar, and They Aren't One of the 24 Solar Terms
Many people assume Sambok is a lunar holiday or one of the 24 solar terms. It's neither. It belongs to a category called 'japjeol,' the miscellaneous seasonal days that are counted separately.
To set Sambok, the calendar uses two landmarks like a compass: the summer solstice (the longest day of the year) and 'Ipchu' (the start of autumn). Traditional day-counting uses ten heavenly stems (gap, eul, byeong, jeong, mu, gi, gyeong, sin, im, gye). From these, you pick out only the days with the 'gyeong' (庚) character, which carries the cool quality of metal.
The third gyeong day after the summer solstice is 'Chobok.' The fourth is 'Jungbok.' And the first gyeong day after the start of autumn becomes 'Malbok.' It's a clever blend of the sun's cycle and an old calendar code.
A Closer Look: Why the Gap Sometimes Stretches to 20 Days
Normally, Chobok to Jungbok takes exactly 10 days. In the ten-stem system, a gyeong day comes around once every ten days. So you'd expect Jungbok to Malbok to be 10 days too. But in many years, it's actually 20 days.
The reason is a rule: Malbok isn't simply the next gyeong day after Jungbok. It must be 'the first gyeong day after the start of autumn.' So if the next gyeong day after Jungbok comes before Ipchu, you skip it, and the one after that becomes Malbok. When there's still plenty of time between Jungbok and Ipchu, one extra gyeong day gets skipped between the two.
A year when the gap between Jungbok and Malbok stretches to 20 days is called 'wolbok' (越伏). In a wolbok year, the Sambok season runs longer. But that's just a result of how the days are counted and has nothing to do with the actual weather. Sambok is the product of a clever counting method, which is why its dates shift every year.
Common misconceptions
Sambok (Chobok, Jungbok, and Malbok) is one of the 24 solar terms.
Sambok is not one of the 24 solar terms. It's a seasonal custom (a 'japjeol') set by counting gyeong (庚) days of the ten-stem cycle, starting from two of the 24 solar terms: the summer solstice and the start of autumn.
Where you meet it
On Chobok or Malbok, long lines form outside samgyetang restaurants at lunchtime as people look for a hearty, energy-boosting meal.
If you look at a calendar, you'll see that the solar dates of Chobok and Malbok shift slightly from year to year.
In one sentence
Sambok is three days so hot that autumn's energy lies down. They're set by counting gyeong days after the summer solstice and the start of autumn, and they've long been a way to beat the heat.