What does a dollar sign in a file name means?

A dollar sign ($) in a file or folder name makes it hidden. If you are trying to map a network drive or folder be sure to type the fulle name including the dollar sign ($) otherwise you won't be able to map to the network drive. For example, say the folder "MyFolder$" lives on a server named "MyServer". If you want to map to "MyFolder$", you would type this in the folder name field of the "Map Network Drive" dialog:

\\MyServer\MyFolder$

If you just type:

\\MyServer\MyFolder

The map will fail.