Let’s start with what an easement is: An easement grants someone a right to do something on someone else’s property. For example, PECO has an easement on a corner of my property in Philadelphia. There is a power pole in the easement. PECO has the right to place a power pole in that corner of my property. If you have a property that has no access to a public road, you might have an easement on a neighbor’s property granting you the right to have a driveway, power lines and gas lines cross their property to the road.
A conservation easement is a way to restrict development in an area. A farmer or airport owner might find their property is worth so much to a developer that they could sell it and retire. However the community or a conservation group might want to keep the farm from being developed. So they approach the farmer with a deal. They give the farmer money and in return the farmer gives them an easement that prohibits building homes on it. It is now worthless to the developer. The farmer can continue to farm. And the farmer pockets a nice chunk of change. The farm can be sold, but it will remain a farm.