Simply put, a whistleblower is a person (usually an employee) who informs on a person or organization engaged in an illicit activity. In most cases, a whistleblower reports on fraud, waste, abuse, corruption or dangers to public health and safety to someone in a position to rectify the wrongdoing.
Whistleblowers have been known to expose illegal and secret practices at big businesses, or in the political realm. Some of the most famous whistleblowers are Mark Felt (Watergate), Edward Snowden (NSA) and Linda Tripp (Clinton/Lewinsky scandal). While these cases spotlight whistle blowing on a national level, illegal activities can happen in any business atmosphere.