I have Yosemite 10.10.1, after the upgrade my Cal has a 1 in a red dot on it, like there is message or something. What is this? I updated to Yosemite 10.10.1.  I sent an invitation to a colleague.  Now I have a Red Dot with 1 in it on my iCAL icon.  I deleted the invitation, but the Dot and one remain. Does anyone know what this is?
Go to help topics and the answer is there. It happens when someone invites you to an event and you have not accepted yet. In the top left corner of the calendar screen there is a symbol that looks like a u with an arrow pointing downward, Click on this and the events appear asking if you want to accept or decline. one you complete the number disappears.