Consolidation, merger, amalgamation are comparable when denoting a union of two or more business corporations.
Consolidation is often used as a general term; more precisely it implies a unification of the companies or corporations with dissolution of their separate corporate identities and transference of their combined assets, franchises, and goodwill to a single new corporate unit, often under an entirely new name.
Merger usually implies a unification in which one or more companies or corporations are absorbed by another and the assets (as property, franchises, and goodwill) of the former are transferred to or merged into the latter whose corporate status and name remain unchanged. In a merger additional shares of stock may be issued by the absorbing company or corporation to replace on an agreed basis the shares of the units absorbed or a monetary transaction may be involved.
Amalgamation is often used interchangeably with consolidation in its general sense and applied to any form of consolidation or merger. It is sometimes restricted to a consolidation in which a new corporation with an entirely new name and corporate identity results or, in British use, to a union of the merger type.