Tortious interference is when one party interferes with the contractual or business relationships of another party. In order to qualify as tortious interference, the interfering party must act deliberately to interfere with the other party.
In the context of the law, tortious interference is a civil wrong and plaintiffs can seek damages for it.
There are a number of different things that can qualify as tortious interference. For example, blackmail, inducement, implied use of force and other unethical practices can all be tortious interferences.
When a party commits a tortious interference, it is generally because they have a financial interest in sabotaging a particular contract or agreement. This could be because they don't want to face the competition, because they want the business for their own company, etc.