"Right of way" means: who has the right to drive through an intersection or road first.
For example, fire engines and ambulances always have the right of way.
Cars facing a green light have the right of way at an intersection over cars that have a yellow or red light.
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A "Hydro right-of-way" means: the land under a high voltage hydro-electric line (wires).
There is a law that hydro lines have the right-of-way; this means that you cannot use the land for anything else, and you cannot block the hydro lines. If you own a piece of land and the government wants to run hydro wires across your land, you cannot stop them.
It is also illegal in Ontario, Canada to build a building under a hydro right-of-way, because the electrical field may have a negative effect on the health of persons nearby.