What Does "this" Refer To In A C# Method Signature

I've been watching the ASP.NET MVC Storefront video series again and saw something that I've never noticed or payed any attention to before. I noticed there were a lot of references to this in the signature lists of various methods. Here is an example of one:

public static Category WithCategoryName(this IList<Category> list, string categoryName) {
return (from s in list
where s.Name.Equals(categoryName, StringComparison.InvariantCultureIgnoreCase)

[code]....

First of all, I'm not totally sure why <System.Runtime.CompilerServices.Extension> _ was included, maybe it's just the converter, nevertheless, as you can see, this wasn't converted into anything that I can tell unless it has to do with the aforementioned <System.Runtime.CompilerServices.Extension> _.What does this actually refer to and/or do in the C# method signature?Is there a VB.NET equivalent?

So we've definitely clarified that this does in fact denote an extension method and that from the answers given, it seems there's no inline VB equivalent. I would like to add that since I mentioned the ASP.NET MVC Storefront video, the C# example above was pulled from his CategoryFilters class. I assume this is how you implement what was referenced as a pipes and filters or pipeline methodology.I assume VB.NET's way of handling extension methods is something like this for example:

Imports System.Runtime.CompilerServices
Public Module StringExtensions
<Extension()> _

[code]....