It is a public declaration of beliefs and intentions, a movement announcing to the world what it stands for and what it means to do. The word means to make manifest, to bring into the open.
A manifesto is a published declaration of the principles, aims, and intentions of a person, group, or movement. It is meant to be public and bold, putting beliefs on the record and calling others to join or act. The word comes from the Latin manifestus, clear or evident.
It is a tool of movements and founders alike. The Declaration of Independence is, in a sense, a manifesto: a public statement of principles and grievances declaring a new course. Political and artistic movements throughout history have announced themselves with manifestos.
Its force is in clarity and commitment. A manifesto does not hedge. It states what is wrong, what is wanted, and what will be done, planting a flag that supporters can rally to and that history can hold the authors to.
It can serve any cause, for good or ill. The manifesto form has launched liberation movements and revolutions, but also extremist and violent ones. The format is neutral; what matters is what is declared and what is done in its name.