Definition of acquisition: To gain control over another firm, usually through the purchase of shares of the company or to buy assets of the business directly.
Acquisition may involve a takeover where one firm buys out another, often against the wishes of certain taxpayers. People may talk of an acquisition when there is a mutually agreed merger – in which two firms of equal standing decide to come together to form one firm.
In practise there is often a blurring of the distinction between merger and acquisition. Generally, an acquisition is a takeover of a firms assets, with some resistance from shareholders. A merger is a mutually agreed decision to make one firm.