What are parallel universes?

I answered this question on Yahoo! Answers and my reply was chosen as the best answer.

A parallel universe is one where everything is the same - we still live on earth, you and me exist and everything else and it is governed by the same laws of physics. The difference come in the path taken by your life basing on a particualr decision that you took.For example - At somepoint in my life I had to make a choice e.g. either pursue engineering or business management. I chose engineering in this Universe and currently I am content with being a software engineer. I took one road of the fork and I am in this universe. In a parallel universe I took the BusinessManagement road of the fork and probably I own a big business in a parallel universe. My assumption is every time you have to make a choice and you choose one in this universe there will always be a story of you running in parallel in the other universes (The number of universes will be equal to the number of choices you have in hand)

Here was the reason why the asker chose it as the best:

This answer is a deeply reflected one and it makes one think about the myriad dimensional universes that oprate in our lives .I will have to think about the isses raised in here. Meanwhile many thanks for your help.