Find me on Discord, nobody1089#3719. I'm in the famitracker.org server as well as SMWC.
If person or group A is perceived to have power over person or group B, and A blocks B from expressing something, and it is believed that A did this because A disapproved of what B was trying to express, A will be be accused of “censoring” B.
Roughly, the first type can be thought of as “not allowing advertisements for the competition in your own store”. Some things that should generally be OK: banning atheists from religion forums; banning Macintosh evangelists from Windows forums; banning creationists from science forums. What should not is banning people from technical forums over their real-world political affiliations and opinions.