Kingsnakes are North American constrictors that eat small animals and eggs. They get their name from the fact that they often eat other snakes, including rattlesnakes and other venomous snakes. They are non-venomous, but are still sometimes considered pests as they will eat eggs and chicks; usually they are tolerated or encouraged in rural settings, as they eat mice, rats, and other pests.
The label 'kingsnake' refers to any member of the genus Lampropeltis, which consists of four species and dozens of subspecies. These snakes are almost always named as a kingsnake (e.g., Speckled kingsnake, Prairie kingsnake) or a milk snake (e.g. Guatemalan milk snake, Mexican milk snake), and some may be known as either depending on local dialect, e.g. the scarlet kingsnake AKA scarlet milk snake.
For many Americans, the most famous members of this group are the scarlet kingsnake, Mexican milk snake, and red milk snake, as these are the three with bright red, black, and yellow stripes, making them easy to confuse with the very venomous coral snake.