As far as I am aware there isn't a clear cut definition for this.

In general though an Islamic fund is one in which the cumalitive funds will only be invested in assets and securities that are deemed to be halaal (by the fund manager usually so this definition can vary). In addition most Islamic funds will also ditrubute the profits in accordance with Sharia'ah.

A non Islamic fund will invest in all assets and securities regardless of whether they are halaal or not and the distribution of profits does not have to comply with Islamic jurispudence either. Typically non Islamic funds will use a high proportion of derivatives, options and futures contracts in order to leverage the fund as highly as possible however all of these types of products are haraam. (There are number of companies trying to develop halaal equivalents though).

Hope that helps.