Regarding what to type into the parameter of this given function

Question

Hello, I am just began working on the software development and have few questions about some function as I have not used C# for like a year. Here is my question, In the function at the bottom, I am just wondering what "([Optional, DefaultValue(Constants.SilentLoud.Loud)]" stands for. Is it kinda like a data type? and then, what should I type in to this parameter when I need to call this function? Could you please explain what it stands for and what it does?


The function is:

Public object Close([Optional, DefaultValue(Constants.SilentLoud.Loud)] Constants.SilentLoud silent)


Thank you very much!