Why is the anime named "Baccano!"? The question itself is self-explanatory!
What's the meaning of it? 
And why is it named so? 
How was the anime named so? 
I thought the reason would be revealed by the end if the anime but it didn't, and I'm left here wondering...
As the English Wikipedia article states, Baccano [bakˈkaːno] is simply Italian for "ruckus, row, din".

As far as I remember the story is never set in Italy, however the Mafia-like organizations featured in the Anime are likely what makes the connection here and you will probably agree that there is quite a bit of "ruckus" going on,