• What is #

Question related to mission Palindromic Palindrome

What do you mean "#" ?

I worked on previous task where I couldn't use 'while' 'for' etc. but this one is weird. Templace code doesn't use '#' yet it is rejected so again my questions is what is '#'?

-- edit -- Okay I haven't focused enough on reading task ;P Code should be palindrome itself ech..