Answer:
Sexual harrassment is making offensive sexual comments, making unwelcome sexual advances, touching someone sexually against their will, threatening to fire/demote someone for not performing sexual favors for a boss, offering to promote someone if they will perform sexual favors for a boss.
Gender discrimination is refusing to promote someone or hire someone or paying someone less money FOR THE EXACT SAME JOB because of that person's gender. IT is only gender discrimination if the person COULD do the job as well as the current employees, but is not given the opportunity. (Example: until recently, women could not serve on submarines in the US Navy)
It is NOT gender discrimination that there are no women in the NFL because women would NOT have the same size/strength as a male football player....except maybe for the kicker and punter since players are NOT allowed to tackle those players.