I have a market exchange simiulation which carries out trading activities such as bidding for and offering trades. I have to decide when and how to generate bids using a defined algorithm which takes account of the current and likely future market price. I'm not sure what they mean by defined algorithm. I think just comparing the current market price with the future to see if it increases/decreases should be able to get the job done but I'm not sure if that's what they want by asking for a defined algorithm.
I would say that "defined algorithm" is simply one that you write that operates according to a defined set of rules. i.e. Not only do you need to define when to buy, but also when to sell; when to take a profit, verses continuing to hold and when to take a loss.
If you're writing such an application, you should be able to go back in time and feed it historical prices and see how it does.