I know somewhere it mentions that one should not gamble...would trading in shares be considered business, or gambling with ones own money? Or is gambling only that which the returns are not guaranteed?

I have understood that the prohibition on gambling is mainly when a person counts on winning.

And that the prohibition does not apply in a situation where an eligible entity puts on a gambling event specifically as a fundraiser, where it is expected that those gambling on trips to Israel or Torah books are aware that they are making a contribution to a good cause, and are not in it for the gambling aspect.

Surely there are some who are not comfortable with eroding the prohibition in that way.

katja,

the stock market is a business in which a person desires to invest or end an investement with business x. no different then a friend coming to you with a business plan and you got in on the business only later you desire to sell your portion of the business back to them or to somone else.

when returns are not guaranteed is apart of gambeling but it also goes with business as well. that is why some business goes under do to the lack of a guarantee of success..

what gambling is that of a agreement between two or more people for one or more of them to be rob of their possesion(recive nothing for the cash).

for a more detail answer on gambling you should contact your rabbi.