Dak means chicken in Korean. it’s a stir-fried chicken marinated in sauce. There are various types depending on the sauce, but the most common dakgangjeong is the one with sweet chili sauce.
On the street, it is usually served in a cup. Like this.
Eating while walking down the street with a cup is one of the best ways to feel the Korean atmosphere.
If you press 6:55 seconds, you can see the reaction of an Englishman eating Dakgangjeong.