It commoly accepted the term lobby as equivalent to "pressure group". The term refers to any organization of a social, economic and citizen nature that carries out actions to influence the public powers in defense of the common interests of its members. A lobby is a business association, but also a company, a union, an NGO, a consumer association or a church.
The bad press of the lobbies is born of the practices in the USA, where they finance the political parties and the campaigns of their candidates and then they press in the elaboration of the laws, a model different from the one that exists in Europe. In return, they enjoy a reputation for efficiency. President Kennedy is credited with the phrase :the lobbyists make me understand a problem in 10 minutes, while my collaborators take three days.