roots of grass; hidden places
Literal meaning: the roots of grass. Figuratively, it refers to places hidden from sight or hard to find, often used in the set phrase 草の根を分けて探す (search high and low).
See also: 草の根を分けて探す
They searched for the criminal as if combing through every blade of grass.
Common in political and organizational contexts, referring to the ordinary members or local level of a movement, as opposed to the leadership.
The political party is trying to expand its grassroots support.
Grassroots movements can sometimes change society.