Text Filegroup, Filegroup and Filestream filegroup. What's the difference?

Most of all, I'm not clear on the distinction between Text Filegroup and the other two.

I understand that a 'standard' filegroup can hold user and system data, and that ideally a secondary filegroup should be created and set as default to separate user data from system tables. I also understand that BLOB data in filestream columns will be stored in the filestream filegroup. But where does Text Filegroup come in?