A more thorough explanation:

Definition: Boston interest refers to an object of human desire, especially financial advantage or profit. It can also refer to a legal share or right in property, which includes any aggregation of rights, privileges, powers, and immunities.

Examples:

• Absolute interest: An interest that is not subject to any condition.
• Beneficial interest: A right or expectancy in something, such as a trust or an estate, as opposed to legal title to that thing.
• Contingent interest: An interest that the holder may enjoy only upon the occurrence of a condition precedent.
• Controlling interest: Sufficient ownership of stock in a company to control policy and management, especially a greater-than-50% ownership interest in an enterprise.
• Defeasible interest: An interest that the holder may enjoy until the occurrence of a condition.
• Equitable interest: An interest held by virtue of an equitable title or claimed on equitable grounds, such as the interest held by a trust beneficiary.
• Entailed interest: An interest that devolves through lineal descendants only as a result of a fee tail.
• Entire interest: A whole interest or right, without diminution.
• Expectation interest: The interest of a non-breaching party in being put in the position that they would have been in had the contract been performed.

For example, a person with a beneficial interest in a trust receives income from the trust but does not hold legal title to the trust property. Another example is a controlling interest, which refers to sufficient ownership of stock in a company to control policy and management, especially a greater-than-50% ownership interest in an enterprise.