Agency is the act of delegating a transaction (muʿāmalah) that a person has the right to perform himself to someone else so that he may perform the task on his behalf. The transaction may be a contract (ʿaqd) or a unilateral instigation (īqāʿ)[1] or something related to these, such as handing over and taking possession of something. For example, a person may appoint an agent (wakīl) to sell his house for him or marry him to a woman. Therefore, someone who is foolish with finances (safīh)[2] cannot appoint an agent to sell his house for him as he does not have right of disposal over his property.
-Ayatullah Sistani, Practical Laws of Islam, Agency ((Wikalah)
The difference between a ‘contract’ and a ‘unilateral instigation’ is as follows: with a contract, two parties are required – one to make the offer and the other to accept it. Marriage, therefore, is an example of a contract. In contrast, in a unilateral instigation, one party alone executes the transaction, as is the case with divorce.
Ruling 2091 provides further clarification of this term: it refers to someone who spends his wealth in futile ways.