What is failure?

Dictionary.com defines failure as:

1. an act or instance of failing or proving unsuccessful; lack of success: His effort ended in failure. The campaign was a failure.
2. nonperformance of something due, required, or expected: a failure to do what one has promised; a failure to appear.

Basically, failure is either the absence of success or the state of something that does not meet expectations.  Can a project fail if expectations were not clearly stated at the beginning? Or if its criteria for success were not defined?

Success can happen outside of expectations

Sometimes the expectations we have at the beginning of the project become irrelevant as the project evolves. For example, a research project where the initial expectation of is to develop a drug to treat a specific condition, but that drug ends up as a better, more effective treatment for another health problem. Can this project be seen as a failure? There is still success, even though the end product does not meet the initial expectations.

Success and failure are in the eyes of the beholder

Some projects go well. Some projects go badly. At the end of the project, a lot is forgotten, and what is seen is the end result. So even if it was excruciatingly difficult to deliver, the project can still be seen as a success if the end result is seen as positive.