Sexual discrimination treating someone less favorably than others in their terms and conditions of employment, based on gender, sexual orientation or sexual preference.  Any such consideration in decision making is unlawful, even if it is not the only consideration.  

Sexual harassment is either establishing terms and conditions of employment that require sexual favors (called quid pro quo sexual harassment), or creating, maintaining, or tolerating a sexually hostile work environment.  Just how hostile, offensive, or abusive the environment must be to support a cause of action is still a matter of legal dispute and controversy.  Typically, conduct can be actionable under state or federal law even if it is not so severe as to cause a plaintiff-employee to suffer psychological injury.