How do I get that window back?

I couldn't find it anywhere on the menus but then I don't know what it's called. When you have a track selected you're supposed to have another narrow window on the left that shows track, clip, Pro Channel. You can assign the bus of a track and adjust pan and things like that. I probably hit some key that closed that window without knowing what it is and I want it back. How do you get it back and what is it called?