A consulting or consultancy firm is a business of one or more experts (consultants) that provides professional feedback to an individual or an organization for a fee. The types of firms vary, such as technology and advertising firms.
Consultancy firms target company executives and provide them with consultants, also known as industry-specific specialists and subject-matter experts, usually trained in management or business schools. The deliverable of a consultant is usually advice or a recipe to follow to achieve a company objective, leading to a company project.
More and more consulting firms are complementing the strategic deliverables by providing the means to implement the recommendations, either with the consultants themselves or by providing technicians and/or experts. This has opened up new markets for these companies. This is called outsourcing.
Ref : Wikipedia