What is Aleatory Contract?

Legal Definition
Civil law. A mutual agreement, of which the effects, with respect both to the advantages and losses, whether to all the parties, or to some of them, depend on an uncertain event. Civ. Code of Louis. art. 2951.

2. – These contracts are of two kinds; namely, 1. When one of the parties exposes himself to lose something which will be a profit to the other, in consideration of a sum of money which the latter pays for the risk. Such is the contract of insurance; the insurer takes all the risk of the sea, and the assured pays a premium to the former for the risk which he runs.

3. – 2. In the second kind, each runs a risk which is the consideration of the engagement of the other; for example, when a person buys an annuity, he runs the risk of losing the consideration, in case of his death soon after, but he may live so as to receive three times the amount of the price he paid for it. Merlin, Rep. mot Aleatoire.
-- Bouviers Law Dictionary
Legal Definition
A mutual agreement, of which the effects, with respect both to the advantages and losses, whether to all the parties or to some of them, depend on an uncertain event. Civil Co.de La. art. 2982; Moore v. Johnston, 8 La. Ann. 488; Losecco v. Gregory, 108 La. 648, 32 South. 985. A contract, the obligation and performance of which depend upon an uncertain event, such as insurance, engagements to pay annuities, and the like. A contract is aleatory or hazardous when the performance of that which is one of its objects depends on an uncertain event. It is certain when the thing to be done is supposed to depend on the will of the party, or when in the usual course of events it must happen in the manner stipulated. Civil Co.de La. art 1776.
-- Black's Law Dictionary