Holiday events consist of three different kinds: Seasonal, Yearly, and Themed.
Yearly events occur once a year on specific days or weeks to celebrate the holiday. They are generally either themed around the event or are just a general event to celebrate the occasion.
Themed events are just events that are themed around the holiday, and don't always happen every year.
Seasonal events happen every year and include festivals! They last a few months and have a bunch of fun prompts or activities included in them, as well as a prize booth where you can get themed items and limited traits and familiars for holiday currency.