Discrimination is a content descriptor only used in PEGI 18. It signals that there are themes in the video game that may encourage hate or discrimination towards certain minority groups. Discrimination is having belief of a negative stereotype of a group of people over a basic trait that they have no control over and can't change. Then projecting the hatred from these beliefs to harm these innocent peoples/groups. This includes race (racist), gender/sex (sexist), age (ageism), country of origin (xenophobia), religion, disabilities (both viable and invisible), LGBT, etc.
This label only seems to apply of the discrimination being shown in the game is presented as a positive / morally good belief to the player (hate speech). Since most media presents discrimination/hatred as a negative / very harmful, this descriptor is usually not applied. This descriptor is extremely rare; of the thousands of titles submitted to the PEGI for a rating, only five have ever been given this descriptor, and it was most recently given to SWAT: Target Liberty in 2007.