Clear explanation of Conflict of Interest with examples in journal articles
I recall having seen some papers (say, on a method of electrode modification), where an author has been a shareholder in a company implementing this method on an industry scale, commercially. This is an example of a COI; a person is gaining money from another entity (in this case, his company) working in the same sphere.

Here's what I found on the web.


  A potential conflict of interest exists when an author has a direct or indirect relationship, through the research-sponsoring institution, with a company that may benefit from the results of the study. The following types of relationship are considered as potentially conflicting and must be disclosed: 
  
  If over the past two years one of the authors: 
  
  
  Received fees for consulting services, delivery of lectures and text writing or payment for any other type of service rendered to the manufacturer of the product. 
  Received any kind of contribution from the manufacturer of the product (funds for the project, equipment, drugs, personnel) related to the project under analysis or any other involving the same product. 
  Received funds from the manufacturer of the product to participate in congresses/conferences. 
  Owned stocks in the company that manufactures the product. 
  Is employed by a company that may direct or indirectly benefit from the results of the study. 
  The manufacturer of the product has been involved in data collection, analysis, interpretation or writing. 
  


My example falls under 'owned stocks' part.