A conflict of interest is a situation in which a person or organization is involved in multiple interests (e.g., financial or otherwise), one of which could possibly corrupt the motivation of the individual or organization.
A widely used definition is: "A conflict of interest is a set of circumstances that creates a risk that professional judgement or actions regarding a primary interest will be unduly influenced by a secondary interest."
Primary interest refers to the principal goals of the profession or activity, such as the protection of clients, the health of patients, the integrity of research, and the duties of public office.
Secondary interest includes not only financial gain but also such motives as the desire for professional advancement and the wish to do favors for family and friends. Conflict of interest rules usually focus on financial relationships because they are relatively more objective, fungible, and quantifiable. The secondary interests are not treated as wrong in themselves, but become objectionable when they are believed to have greater weight than the primary interests.

The conflict in a conflict of interest exists whether or not a particular individual is actually influenced by the secondary interest; it exists if the circumstances are reasonably believed (on the basis of past experience and objective evidence) to create a risk that decisions may be unduly influenced by secondary interests.

Adapted from Wikipedia, the free encyclopedia. Internet. Accessed on June 14, 2016.