Lightroom is expanded to fit my entire screen

[TTIPhoto]

Lightroom fills my entire 27" Mac screen. I dont want it to, how can I resize it?

[Conrad C]

It sounds like Lightroom accidentally entered Mac full screen mode. You can enter or exit that mode the same way you would for any other application that supports Mac full screen mode. For example, move the mouse to the top edge of the screen to reveal the menu bar and window title bar, then click the green window button in the top left corner of the window title bar.

For details, see this Apple article:

Use apps in full screen on Mac