A merger occurs when one company is absorbed by another, while an acquisition takes place when a larger company takes over the shares and assets of a smaller company. Mergers and acquisitions allow companies to achieve economies of scale, gain market share, and increase competitiveness. However, they can also lead to integration difficulties and excessive debt if not managed properly. Some major mergers and acquisitions in India include the Reliance-BP deal, Essar exiting Vodafone, and Vedanta acquiring Cairn India. Reverse mergers allow private companies to go public by acquiring shell public companies.