What are the winter solstice and the summer solstice?

In the Northern Hemisphere, between the equator and the Arctic Circle, the winter solstice indicates the beginning of winter and occurs when the sun rises and sets on the horizon farthest south for the year, and daylight length is at a minimum, ranging from 12 hours and 8 minutes at the equator, to no sunlight at all at the Arctic Circle. (In the Southern Hemisphere the summer stolsice occurs on this same day.)
In the Northern Hemisphere, between the equator and the Arctic Circle, the summer solstice occurs when the sun rises and sets farthest north on the horizon for the year, and the length of daylight is maximum, ranging from 12 hours, 8 minutes at the equator to 24 hours at the Arctic Circle. (In the Southern Hemisphere, the winter solstice occurs on this same day.)

Source: Chase's Calendar of Events 1998, pp. 332, 619.