what does "Khulaa Khat" [open letter] mean?

Re: what does “Khulaa Khat” [open letter] mean?

video link ‘Beema’ ke istemaal ke liye tha. Refer posts 5, 7 & 9.

Ab aakhri tukka! Yeh shair dilli fatah hone ke bad ke halat ki taraf isharaa karta hai ke her taraf bus tabahi o barbadi ki khabar sunai de rahi hai.