Insider trading is the buying or selling of a company's stock by someone who has material information of the stock that is not public information.
This information can be anything like a quarterly result, a project failure, etc. You cannot take any trades based on information that hasn't been released to the public yet.
An insider is a director, senior officer, promoter of the company, or anyone owning more than 10% of the voting shares of a company.
Every country has there regulatory authority to prevent insiders from engaging in insider trading.