What one row of the air-quality table is
datasets::airquality has 153 rows, and ozone is missing on some of them.
What is one row, and why is a model that uses ozone not a model of all 153 days?
Worked answer
One row is one day in New York from May through September 1973. A day with missing ozone is still a day in the table. A model whose formula names ozone drops that day, because the fit cannot use a response it does not have. The analysis sample is the set of days the fit actually used, and nobs reports that count. Quoting the result as a description of all 153 days describes a different set of days from the one that was fit.