In continue to the definition by Spiel Brickner, which was rather accurate, I'
d like to add a couple of things.
While using the word "blyat" as a link word (regardless to its meaning) , there are no rules for where to place this word in the sentence. You
may place it anywhere in the sentence as many times as possible, even after each word if you
will, and it
will still remain correct russian grammar.
The bets anology demonstrating it, is the hebrew word "keilu", which northern Israeli
bitches use similary as a link word placing it randomly in the sentence regardless the meaning of the word itself.
(A little exaggerated example, even though you can find russian people
talking this way)
Yesterday blyat I went to this
party, blyat, and it was so lame blyat that even after I got
drunk blyat I didn't feel like dancing blyat.