What is [ and ] in c#?

Question

What is the [ and ] in c#? what is it used for? what does it mean?

example

[DefaultValue(null)]
[JsonName("name")]
public string Name
{
    get
    {
        if (this.name == null)
        {
            return String.Empty;
        }
        return this.name;
    }
}

Answer 1

That is an Attribute. By themselves they do nothing at all, they just decorate code. But code can discover attributes and react to them at runtime.