The shortest day of the year is called the winter solstice. It depends on which year and which hemisphere you mean.
Interpreting your question
Your message ends with “20”, which most likely means you were asking about the year 2020. For 2020 in the Northern Hemisphere, the winter solstice (shortest day) fell on 21 December.
Northern vs Southern Hemisphere
In the Northern Hemisphere, the shortest day of the year occurs on the December solstice, which can fall on 20, 21, 22 or 23 December depending on the year.
In the Southern Hemisphere, the shortest day is the June solstice, which occurs around 20 or 21 June.
If you meant a different year
If you meant a different year than 2020 (for example 2025 or some other year) or a specific location, the exact calendar date can shift slightly, but it will still be the December solstice for the Northern Hemisphere and the June solstice for the Southern Hemisphere.
