Some even say "it is the shortest day of the year".
Unfortunately, that sentence is wrong.
Remember EVERY DAY has 24 hours.
What is correct; is that on the solstice, those who reside in the northern hemisphere have the least amount of daylight, which is not about the length of the day. And the further north you are from the equator, the less light you have been having, every day, until now. As of tomorrow the amount of daylight will slowly increase.
And truth be told, for this year the solstice won't actually occur until 23:03 UTC. UTC is Universal Coordinated Time - that is the time with out any adjustments for regional differences or daylight savings time. This UTC is thought by some to be GMT (Greenwich Mean Time) but that is no longer true.
And for those of you in the southern hemisphere, happy summer solstice.