Assertiveness training refers to instruction in how to be self -assertive. It employs the use of behavioral rehearsal and other techniques to train people to express their needs effectively without infringing on the rights of others.
Moreover, Assertiveness training is a technique to teach clients to effectively express positive and negative feelings to others so that they may achieve desired purposes.
Other /More definition:
Assertiveness training refer to techniques that train people how to be appropriately assertive in social situations; usually included as part of health behavior modification programs, on the assumption that some poor health habits, like xcessive alcohol consumption or smoking, develop in part to control difficulties in being appropriately assertive.
Lexicon of Psychology - Terms, Treatments, Biographies,