The phrase "primary class" refers to the main or most important group or category. It could imply the initial or fundamental level of something. Full definition
The two primary classes of life insurance include term and permanent. (insurancescored.com)
Critics of the Government alleged that reductions in primary class sizes had only been achieved at the expense of class sizes in secondary schools. (politics.co.uk)
In the hour leading up to the 6:30 a.m. led primary class, students are buzzing. (sonima.com)