To be politically correct is to take care not to offend or exclude any person or group. Some people criticize others for being too politically correct.
When you're politically correct, you're careful not to insult people or marginalize them, especially if they belong to a group that's often discriminated against or is in some way at a disadvantage. The term, often shortened to P.C., is commonly used in a contemptuous way: "She's so politically correct that she gets offended by every joke she hears."