quartus main display

Can anybody advise where I find description of the Quartus II main display?

To be explicit, I want to know the meaning of the one-row window in the icon bar, just between the "Redo" button and "Project Navigator" button.

In the Quartus II Introduction file (ftp://ftp.altera.com/up/pub/altera_material/11.1/tutorials/verilog/quartus_ii_introduction.pdf), Figure 10, page 11, it is populated with the word "light".

I went through several tutorials on the web but did not find explanation.

Thanks for help. Jaromir