Substantial interest is a term that applies in many contexts and often isn't capable of a precise definition. It may be defined as a percentage of ownership, but may be more generally used to mean an interest that is not remote or nominal and affects a proprietary or pecuniary interest.
The following is an example of a school board's definition of substantial interest, in the context of a conflict of interests:
Definition of substantial interest: Any interest that is not a remote interest as defined by law and university policy. Substantial interests generally involve pecuniary or proprietary interests. For example:
* Substantial interest in stock would be ownership of more than 3% of the shares of a company and/or more than 5% of your income is derived from this interest.
* If you work in the area of scholarships and have a son or daughter applying for a scholarship, you may not serve on the committee that reviews your child's application.