These two terms are often confused or substituted for each other, however they are two different things.
A “setback” is a limitation on site development which generally requires a building, structure, or other item to be placed at a specific distance from a property line. Sometimes certain items, like landscaping or snow storage, may need to be located in a setback to manage impacts to adjacent property owners.
An “easement” is a portion of the property reserved by agreement by the Property owner that allows access on or through the property. Generally, an easement is specific, allowing access to specific entities or for a specific reason. Common types are utility, drainage, or access easements. Utility easements can be for electrical, gas, water, sewer, cable or telephone lines, whether they are installed above grade, on grade, or below grade. Access easements can contain roads or driveways and may allow emergency vehicles, private parties, or the public access to a property or across a property.
In general, you cannot build anything in an easement, and you may, sometimes and with limitations, encroach or build into a setback.