What is the meaning of ~ while referring path in linux
 

I have seen people using ~/xxx/ddd/

i assume it is used to refer any particular path from anywhere, isn't it?

your home directory

~ - this refers to your home directory.
~xxxx -- refers to xxxx's home directory.

while ~xxxx is users xxxx home, but ~/xxx/ddd is current users subdirectory /xxx/ddd

so if you try: cd ~/xxx/ddd/
it will change to 'current user's home/xxx/ddd subdir ! (if exists)

Let's say that I'm in [@/var/tmp] and I put: "cd ~/torrent" it will change to my home/torrent dir (@~/torrent)

I hope this explains it.