What is positive discrimination? Let me give you a Google example. We want to have more female software engineers work at Google. Sadly, there is only a small fraction of female software engineers at college, and applying for roles. Google has some amazing initiatives to encourage more girls into software engineering and to apply to Google, but even then it's hard to hit the mark.
We want more female software engineers for two reasons: (a) we promote diversity at Google, and thus we really want a good balance of all races, gender, sexuality and so on - we value what differences can bring to the table and (b) we get criticized by people for not employing enough female engineers by people who are not smart enough to see that we bat above average in the department, given the small pool of females available.
So here's the tricky part. Two engineers apply for a job, and they have exactly the same qualifications, do just as well in the interview. One is male and one is female. Who gets employed. Well the female one. Even if the male is slightly more qualified it's more beneficial to employee a female one to help encourage diversity.
If you are the male who is rejected this may seem unfair. If you are in leadership, you will deny this "positive bias" exists - we want to pretend we'll always hire the most qualified candidate, and if any bias exists it's that we want to reduce our high rate of false positives (people who probably deserve to work at Google but maybe got unlucky and didn't do so well in an interview)..... but we want to be expecially sure not to have a false positive where the candidate is female, or from some racial minority group.
We want to improve diversity. I don't like how we beat around the bush however. A friend described it best: positive discrimination exists to help bring something into a more favorable balance. Over time, if more females are pulled into software engineering, other females will see this, and more girls will follow the trend. In theory, we'd eventually reach a more fair balance where we are getting a healthy number of applicants from all works of life (not just white males etc) - meaning each team has a wonderful diversity of thought and backgrounds - and there is less need for positive discrimination in future interviews.
This is just my 5 cents. I am really proud to work at Google, and it bugs me when we get criticized for not enough females or particular groups. I feel like we are doing all the right things to encourage more diversity... including talking about issues like this.