pyramid scheme or not?

I am a student and want to start a website that allows students to see
what's happening on the local club scene and also allows them to upload
photos and video clips. Only registered users would be able to access the
content. I want to make this a subscription service where users would pay a
fee every month for example R40,00 per month. What I want to do to try get
users, is to say that, for every user you introduce half there subscription
would be credited to your account every month as long as they stay a member.
This would also allow the students to make some money. I know a pyramid
scheme is illegal. Would what I want to do be seen as a pyramid scheme? and
what is a pyramid scheme exactly?

It is normally not a pyramid scheme if there is a real service and product and people are truly paying for that product--not just to get a new member.