From KDE UserBase Wiki

Calendar Handling

KOrganizer uses so-called iCalendar files to store your data. iCalendar is an open standard for calendar data. In addition to iCalendar KOrganizer also supports the vCalendar standard.

Both standards are supported by a variety of other calendar programs and also some devices like mobile phones.

KOrganizer is able to directly load the files and work with them in a network-transparent way. This allows you, for example, to have only one calendar, which is accessible from the office and from home without the need for copying or syncing.