Q:

What is the meaning of "block special"?

I tried this command on my Linux Ubuntu prompt in Amazon Web Services
sudo file /dev/xvda1

and the output is
/dev/xvda1: block special 

What is the meaning of block special in the output?

A:

Most of the things you find below /dev are either "block special" or "character special" things, and you rather to not change them manually. Your example shows a disk drive partition provided by Xen (what on a "normal, nonvirtual machine" would be /dev/sda1). 
For more details on this special device, please see What is the “/dev/ xvda1 ” device?
For more details on what devices, and especially block devices are, you may consult Device file - Wikipedia, the free encyclopedia.

