How would you call it?

I use them interchangeably, since they mean the same thing. It's all about preference.

But, generally speaking, in Unix it's "directory", in Windows "folder" and in Linux just pick one.

edit: I changed your poll to make it a public vote

simply dir but I rarely have to do with users

This is one area where both UNIX/Linux and Windows users have the same understanding.

It means the same thing, so who cares?

Depends who I am talking to.

The word "folder" is from the Microsoft Windows world where you can also find words like "container" and "desktop". The help text displayed by the Microsoft MSDOS "DIR /?" command only uses the term "directory".