The point of no return is the point beyond which someone, or some group of people, must continue on their current course of action, either because turning back is physically impossible, or because to do so would be prohibitively expensive or dangerous. It is also used when the distance or effort required to get back would be greater than the remainder of the journey or task as yet undertaken.
A particular irreversible action (e.g., setting off an explosion or signing a contract) can be a point of no return, but the point of no return can also be a calculated point during a continuous action (such as in aviation).
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Crossing the Rubicon is a metaphor for deliberately proceeding past a point of no return. The phrase originates with Julius Caesar's invasion of Ancient Rome (January 10, 49 BC), when he led his army across the Rubicon River in violation of law, thus making conflict inevitable. Therefore the term "the Rubicon" is used as a synonym to the "point of no return".
http://en.wikipedia.org/wiki/Crossing_the_Rubicon
