Or summer solstice, if you happen to be in the southern hemisphere.
The December solstice happens at the same instant for all of us, everywhere on Earth. This year the solstice occured on Tuesday December 22nd at 04:49 GMT (Universal time). For us in the US Central Time Zone, it occurred at 10:49 CST last night.
The winter solstice happens every year when the Sun reaches its most southerly declination of -23.5 degrees. In other words, when the North Pole is tilted furthest – 23.5 degrees – away from the Sun, delivering the fewest hours of sunlight of the year.