Term Definition: Start Event
Main Description

A Start Event indicates where a particular Process will start. In terms of Sequence Flow, the Start Event starts the flow of the Process, and thus, will not have any incoming Sequence Flow. A Start Event can have a Trigger that indicates how the Process starts: Message, Time, Rule, Link, or Multiple. The Start Event shares the same basic shape of the Intermediate Event and End Event, a circle but is drawn with a single thin line.

This term can be found in the OMG  Business Process Modeling Notation, V1.2 (Beta 3)  specification http://www.omg.org/docs/dtc/08-02-07.pdf