en masse
In one group or body; all together. For example, The activists marched en masse to the capitol. This French term, with exactly the same meaning, was adopted into English about 1800.
the masses
The body of common people, or people of low socioeconomic status, as in TV sitcoms are designed to appeal to the masses. This idiom is nearly always used in a snobbish context that puts down the taste, intelligence, or some other quality of the majority of people. W.S. Gilbert satirized this view in the peers' march in Iolanthe (1882), in which the lower-middle class and the masses are ordered to bow down before the peers. Prime Minister William Gladstone took a different view (Speech, 1886): "All the world over, I will back the masses against the [upper] classes." [First half of 1800s]