A calendar event is a (self defined) note that you can add to the timeline of an animal. For instance when an animal is treated for a decease. Velos already has some predefined events that are based on production (for example 'in lactation'), and on reproduction (for example 'dry off'). Besides these events, custom events can be added. See How can I add a custom event? for more information about adding a custom event.
A calendar attention is an alert that is generated when a calender event is planned or calculated, for example a pregnancy check or an attention when an animal is not inseminated after the voluntary waiting period. The calendar attentions can be used as a checklist or a to do list. See Which calendar attentions are available to me? for more information about the types of calendar attentions, and how to change these attentions.