What's the meaning of 'trigger warning'?

[Kiwi]

What does 'trigger warning' means?
I see it in some topics but I don't know what's the meaning of it. Please can someone explain to me?
Sorry if it sounds a dumb question but I'm Italian.

[Umiko]

trigger warning is used as a warning that the contents of the topic may trigger either dysphoria or bad urges.

[Kiwi]

I understand now, it's a warning so you should be careful with those topics.
Thank you for answering.