What is Mass ?
Mass is (noun) 1. a large number or large quantity of things Masses of people went to the exhibition. A mass of leaves blew onto the pavement. I have a mass of letters or masses of letters to write. 2. a Catholic communion service She’s a strict Catholic and goes to mass every week. (verb) to gather in large numbers The rebel army is massing on the border. Synonym assemble (adj) involving a large number of people They found a mass grave on the hillside. The group is organising a mass protest to parliament. Synonym general
source: Easier English, Student Dictionary Upper Intermediate Level