A beneficial owner is a person who wields control over an asset, even if it is someone else's name. It can also mean any individual or group of individuals who, either directly or indirectly, have the ability to influence the transaction decisions regarding a specific security, such as shares in a company.
The Financial Action Task Force defines a beneficial owner as:
the natural person(s) who ultimately owns or controls a customer and/or the natural person on whose behalf a transaction is being conducted. It also includes those persons who exercise ultimate effective control over a legal person or arrangement. Reference to “ultimately owns or controls” and “ultimate effective control” refer to situations in which ownership/control is exercised through a chain of ownership or by means of control other than direct control. This definition should also apply to beneficial owner or a beneficiary under a life or other investment linked insurance policy.
An well known example is the Panama Papers, where the registered owners were staff off a Panamanian law firm, even though the actual owners, "beneficial owners" were the firm's clients.