A call out, would be anything that directly targets someone(s) with the intentions of being malicious. IE "The staff is XXXX" "This player is XXXX". content is moderated, and action is taken if necessary on a per case basis.
Just avoid being toxic and if you do have some *feedback* try thinking constructive.
Doesn't that mean that challenging someone publicly politely isn't a callout? For example, "Harmless_Kittens, are you dude enough to fite me 1v1 tomorrow night at 8 PM Pacific?" isn't toxic or malicious, whereas "Harmless_Kittens, you are super skrub, come fite me I am so strong kekeke noob" is.
Are both considered callouts?