A speaker's corner is a special place where people can come and stand on a little box or stepstool to talk to other people who want to listen. It's kind of like a stage where anyone can say whatever they want, as long as they don't hurt anyone else with their words.
In some places, like London, England, there are special parks where people can go to a speaker's corner and speak their mind. People who go there might be talking about all kinds of things, like politics, religion, or just what they had for lunch.
The idea behind the speaker's corner is that everyone should have the right to say what's on their mind, even if other people don't agree with it. That way, everyone can learn from each other and maybe even change their minds about something. It's a way to promote freedom of speech and a healthy exchange of ideas.