The who's out? widget displays a list of all staff members who are out of the office on that day and when they are due back. This will include:
Holidays
Custom absences
Sickness
Remote working
However, you will not be shown the reason for their absence. If you would like to view this information, you can head over to the calendar to view the absences types. Please note that you will only be able to view other people's absences in the calendar if your company settings allow you to. Read more about calendar permissions here.