"Playing xx Tracks-Undo"

When I start to play a song, this message comes up: “Playing xx Tracks-Undo”, with the “undo” highlighted and “clickable”. What does this mean/do? TIA. Wyatt

This button shows up when you issue a Play command that clears your current Queue. Hitting “Undo” cancels the command and preserves the previous Queue.

Cool, thanks!