Refers to situations where a third party wrongfully interferes with a commercial dealings of another. Tortious interference with contract (or contractual advantage) arises where the accused caused one party to break a contract with another, usually by wrongful or unfair means. Tortious interference with business relations (or with prospective contract) means the use of wrongful means to drive a customer or customers away from a party. Frequently tortious interference involves some sort of trade libel or defamation, or alternately improper gratuities or inducements.
Interestingly, most word processing spell checkers do not include the adjective tortious and hence frequently correct it to tortuous – but this later term relates to torture and not tort.