said by jvanbrecht :

It's called right of way (or something similair). It allows public utilities and entities that the local commision allows, to run service lines (power, comm, sewage, water, etc) right through your property, with little discourse for the home owner.

said by cdru :

It's called a utility easement. In a urban and suburban setting, there is almost always a utility easement along the front and back edges of a property, and sometimes in the middle. The homeowner owns the land, but they are forbidden from restricting access. Also any structure (such as a fence) or landscaping may be subject to damage if it interferes with a utility servicing the line.