What does "toast" mean?

A small informational message that pops up like toast.

http://en.wikipedia.org/wiki/Toast_(computing)

It's a type of Window that "pops up" like toast:

http://msdn.microsoft.com/en-us/library/ms632289%28VS.85%29.aspx

An example of a Messenger toast is the message that appears on a user's desktop when one of the user's contacts signs in. Another example of Messenger toasts is the messages displayed when a user receives an alert from the .NET Alerts service. The following are examples of typical toasts: