Legislation: The laws of the land start in city councils, the State Legislature, and Congress. Legislators, influenced by constituents, protestors, and lobbyists, have bills drafted, reviewed by a committee, and voted on by the full body. For example, the 501(c) section of the tax code, that grants nonprofits their tax-exempt status, was created by an act of Congress.
Rule or Regulation: Laws do not always give specifics on how they are to be administered, which is why departments, divisions, agencies, and commissions are granted rule-making authority. For example, according to Utah law a nonprofit must receive a charitable solicitation permit from the state before asking for donations. To administer that law, the State Division of Corporations has created a process, or a set of rules, that nonprofits must follow to receive a permit.
Issue or Cause: An issue or cause is an item that doesn't necessarily have a specific piece of legislation or regulation motivating people to organize. They generally are societal issues. For example, the protests that were sparked by George Floyd's death seek an end to police brutality and other forms of racism.