What is rigor?

Larry Ferlazzo,  whose fascinating and  prolific blog activity leads me to believe he has found the secret of living life without sleep asks the question "What is rigor?"
This was my response in the comment section:


The principal asked that very question at a faculty meeting and the teacher next to me leaned in and said. “isn’t that what happens to a dead body?”

To me true “rigor” is the level of work just a bit above any student’s comfort level. It cannot be an arbitrary concept. I was in a science class the principal was observing. It was a “do over.” The principal wanted a lesson with more rigor then the original one she observed. The students were to read an article on Archimedes and write a summary. The principal had “encouraged” the teacher to pick a” rigorous” article. The students took highlighters and highlighted a variety of random sentences and copied or paraphrased many of them into their summaries. The principal walked around and encouraged them to write more, “good summaries include a lot of details,” she admonished. And they did. The lesson “looked” rigorous, lots of reading, lots of writing. The principal was happy.

I read the summaries- not one person mentioned the principal of displacement. No one could explain the relationship between displacement and mass. The article was above both their reading and science independence level, in my opinion.

So I am afraid that rigor is just a word, a trick, a distraction from the real work of education meeting students where they are and moving them up on the learning curve in a thoughtful, planful way.