Gather in a mass is an expression that refers to the act of people coming together in a large group. The term can be used to describe a variety of situations, such as a protest, a rally, or a large gathering of people for any purpose. The crossword solution for this term is 'CLUMP, ' which is defined as a group of people or things that are close together. This term is often used to describe a large group of people who have come together in one place.