Using (Of T) generic with functions in Visual Basic 2012

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Hi folks,
can you please explain what (Of T) is after function name in following line:

Public Function StdDev(Of T)( source As IEnumerable(Of T), selector As Func(Of T, Decimal)) As Decimal

I am using visual basic 2012 .
I understand that this function will extend IEnumerable(Of T) and gets one delegate as parameter, but I could not get what is (Of T) in this declaration

[!NoItAll]

Of Type
Lets you set the type.
A very common use is
Friend MyList as List(of String)

MyList is now a list of strings. The List class gives you much more control than a simple array has to offer. For example you can use MyList.add("str ing") to add something to the end of the list or MyList.add("Str ing", 2) to add a new element to index position 3. You can also remove items from the middle, etc and all the management is done for you.

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function is declared as
StdDev (Of T)( source As IEnumerable(Of T), selector As Func(Of T, Decimal)) As Decimal

can you please explain what bold text means in the declaration?