An easement is a right obtained by someone to use, or share, the real property of another. Typically, this right applies to a specific portion of your property, not to the parcel as a whole. Its purpose is to accomodate certain needs of a neighbor or of a public agency that are important and cannot be met without an easement. For example, an easement may be sought to pass across your backyard in order to access electric lines.
A private easement is a right negotiated between neighbors. You are most likely to be approached about an easement at the time your house is built or your property is sold, and you are free to grant or deny it. Sometimes the purpose is to allow two homeowners to share a common garage, driveway or other convenience. A private easement is also needed if one person wishes to run pipes or drains under land owned by another. If you grant an easement that later causes conflicts, you may seek to buy out your neighbor's interest in the property.
A public easement grants some right of access and/or usage to a public entity, most often a municipality, power company or water or sewer utility. For example, easements are commonly requested to dig underground water wells, extend sewer lines or place telephone poles. Local governments may seek other types of easements to benefit the community, like the right to use a footpath at the edge of your lawn that leads into a public park. If you deny a public easement, the entity might take legal action.
Most public agencies, institutions and authorities have the power to take over land, structures or other privately owned assets as long as the purpose is to advance community safety or welfare and the owner is offered fair compensation. This power is called condemnation. For example, condemnation could be used by a city in order to widen a road or extend a bridge. If you deny a public easement and the agency begins condemnation proceedings, a judge will hear both sides and render a final decision.