What is the origin of the idiom "grass roots" and when to use it?

The origin of the idiom "grass roots" can be traced back to the 19th century in the United States. It was used metaphorically to describe the grassroots of plants, which are the foundational roots that anchor and nourish the plant, providing stability and sustenance. It is often used when discussing community-based initiatives, social movements, political campaigns, or advocacy efforts that prioritize the active participation and voices of individuals at the local level.