Generally, people assume that being Assertive means being pushy, demanding or asking for self-importance. Assertiveness does not mean being unpleasant to people, getting away with behavior that upsets a team or dictating your terms.
Assertiveness is giving the self, enough respect to become aware and state what one wants and at the same time being sensitive and respecting other's needs too.
Assertiveness can be simply defined as "taking charge of your life"
Assertion is often confused with aggression. Aggressiveness is an act against others whereas assertiveness is appropriate standing up for one's own rights. Assertive behavior is a direct, open, honest, and appropriate expression of one's opinions, values, beliefs, and feelings. Assertive communication demonstrates self-confidence and self-respect in addition to the awareness and respect for other's feelings, opinions, and values.
Assertiveness is based on the belief that you have a right to be listened to and taken seriously, to commit mistakes, to ask for favors and to refuse unreasonable requests without feeling guilty, while at the same time recognizing that the other people also have identical rights.