The phrase "school mass" refers to a religious ceremony or service that takes place at a school where students gather together to worship or pray. Full definition
The rally, started in the aftermath of the Marjory Stoneman Douglas High School mass shooting on February 14, will be held in Washington, D.C. Thousands of students from across the country are expected to be at the rally. (wben.com)
Helena Ramsay, 17, seen in an undated handout photo, was killed in the Marjory Stoneman Douglas High School mass shooting on Feb. 14, 2018. (abcnews.go.com)