[clarkmoody]

In gambling, you stand to lose your entire stake if luck is against you.

In (spot) market movements, your value goes down as the market declines, but you don't stand to lose everything in a moment.

[vec]

Imagine a raffle where tickets cost $1. After the winner is drawn, the house agrees to buy back the first few losing tickets for $0.99, the next few for $0.98, and so on until they work down to $0. The players don't stand to lose everything in a moment, but it's still pretty clearly gambling.