The goodness of fit of a statistical model describes how well it fits a set of observations. Measures of goodness of fit typically summarize the discrepancy between observed values and the values expected under the model in question.
I love it! It's concise and to the point. But do I really want to cite Wikipedia in an article for peer review?
A Google search for the verbatim quote above reveals that this definition appears in countless books, papers, and websites without attribution. Did these authors plagiarize Wikipedia? Did Wikipedia plagiarize these authors? Who knows.
My solution, put the definition in quotes and attach a footnote. "This quote appears verbatim on Wikipedia and countless books, papers, and websites."