In Outlook, you can add over 100 countries' (or religious) holidays. If you want to delete the holidays from the calendar, please follow the steps below:
Step 1: Click the Calendar button from the navigation bar to open calendar;
Step 2: On the Ribbon, click "Change View";
Step 3: Choose "List" from the drop-down list;
Step 4: If you want to delete only one holiday, select the holiday, right click and choose "Delete" from the list;
Step 5: If you want to delete multiple or all holidays, please sort category first by clicking the column header "Categories" to have all holidays together, then holding "Shift" key to select all holidays. Right click and click "Delete" from the list to delete all holidays.