Just to start things of I want to brief you, what a niche is! If you already know what a niche is you can skip this page (but I wouldn't).
First of all we are here in the online marketing world, so when we talk about a niche we don't mean the biological niche. Generally spoken in marketing you will always have a target audience and before you can start marketing you have to define this audience.
Now let's say for example a company sells sunglasses. Than the target market (audience) are people that already have sunglasses (they could break down) and people that want to buy sunglasses ... well we know in reality it isn't easy to identify this but my point is the following: this is not a niche, this is a big market with big and many competitors!
So what's a niche? A niche for example would be wooden sunglasses. Not everybody that wants sunglasses wants wooden sunglasses, it's more specific, more exclusive.
But now back to online marketing: I love movies! So my first site was about movies, but that's not a niche either. So I started with the niche "movie reviews". Honestly this isn't really a niche too... movie reviews of Italian movies, that would be a good targeted niche!
Why can't I pick a brought topic... why do I have to pick a niche?
Well, because we want to make things easier to you! The more specific your niche is and the less competition you have in that niche, the faster and easier you will succeed. Sure you can pick a brought topic, but that won't make things easier.
Just imagine when you go fishing: you go to a big lake with many fishes, but there are already hundreds of others fishing in that lake... So what I would do is go to the smaller lake nearby, but I am fishing alone.