You want to purchase a piece of property. As you review the deed and legal description of the property, you discover that someone else has the right to use a portion of it. Easements are fairly common, but that does not mean that you shouldn't review them to determine how they will affect your use of the property.
An easement allows another party to use part of your land for some purpose. You retain ownership of the property. In some cases, you might continue to use the property, but in others, you may not.