adverbial blocks: description and examples requested

[Terrence Brannon]

I was looking at a line in the hangman program:

  @letters == @solution.grep:{ $_ ne '' }; 

and was told that I was looking at an adverbial block.

But I don't understand what that is and could not find a description
and examples in a reverse search on dev and nntp.perl.org.

I would appreciate any information on this topic.

Thanks