It’s officially called Chat Filtering, and it not only lets you add words to filter, but also whitelist certain words of your choosing. There’s also the option to turn filtering off entirely, which is nice. While initially built into games like Dota 2 and CS:GO, Valve has expanded the feature to the platform’s chat feature itself.
Valve says that this is done because people have different tolerances to words. This allows users to tailor their filters to suit their own needs, rather than having the company apply a blanket standard to every user on the platform. On one hand, this allows for a personalised experience, even if you have to do the personalising yourself. But on the other, one can argue that Valve is being very hands off with Steam again. But either way, the option is now available to all users. To make changes to your own Steam experience, you’ll have to head to the Community Content Preferences page. (Source: Steam)