C# syntax what does it mean

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C#

I have seen this and wondered what it exactly means. Most tutorials and classes just jump over this. For example:

IEnumerable<pie>


I get that IEnumerable is the type but what is the <pie> for?
I see this used all the time, but what i want to know, what does it mean? It doesn't appear to be a type case.

What I have tried:

I've had a number of C# classes, most just gloss over it like it's common knowledge.