The information has to be confidential in its nature, and communicated to someone in such a way as to impose an obligation of confidence. Both of these requirements are determined on a case-by-case by the Courts. Confidential information will normally be commercially sensitive/valuable in some way, and some clear degree of precaution or some other circumstances indicating confidentiality should exist at the time of communication. A private meeting to discuss a business plan in an office building, with a view to making an investment decision, would be a good example of this. Especially if at the meeting it was clear that nobody else was to be told about the plan.
If confidential information is disclosed or misused to the detriment of its owner, there will be a potential claim for breach of confidence.