Following courtesy of https://www.calendarpedia.com/when-is/pentecost.html
Pentecost is the annual Christian festival commemorating the descent of the Holy Spirit on the disciples of Jesus after his ascension from earth to heaven on Ascension Day. It always falls on the seventh Sunday after Easter. Pentecost means "fiftieth day", as it is celebrated on Pentecost Sunday, the 50th day of the Easter season (including Easter Sunday, the first day, in the counting). Some Christian denominations consider it to be the birthday of the Christian church and celebrate it as such. It can fall as early as May 10 and as late as June 13.
Especially in the United Kingdom, Pentecost is also known as Whit Sunday, Whitsun, or Whit, meaning "White Sunday", a name derived from the white garments that were worn by those newly baptized on this day.
Pentecost is followed by Pentecost Monday (also known as Whit Monday), a public holiday in many countries with Christian traditions.