sea of people; huge crowd
Often used in the compound 人海戦術 (human-wave tactics) or to describe a vast, overwhelming crowd. As a standalone noun, it is somewhat literary.
See also: 人海戦術
The area in front of the station was jammed with a sea of people.
They tried to solve the problem by using human-wave tactics.
human wave attack; human wave tactics · throwing people at a problem
Compound of 人 (person) and 海 (sea), literally 'people-sea'. The exact historical derivation is uncertain, but the word follows a common Sino-Japanese pattern for large-scale metaphors.