Legacy is an arrangement made in a testament for someone else's benefit, it is leaving something, of value or not, for someone else, and comes from the Latin, legatus. Legacy is also someone who goes to a special mission, to represent the pope.
In legal terms, in the area of inheritance law, a legacy is when an asset, or several assets, are left to someone else who is not heiress, when the original owner dies, then he leaves all, or part, of his legacy to someone, who may be family, or do not. This person is known as a legatee. The legacy is always left in a will, so there will be a legitimate succession of objects or a sum of money.
A legacy can be constituted by something immaterial. The Roman Empire, for example, left a strong cultural and linguistic legacy that still exists in many societies today. Another example of an immaterial legacy is the intellectual legacy left by many philosophers and thinkers in the past.
Legacy is also when the government of one country joins another, for a certain mission, it is a temporary task, in an extraordinary character.