AVR-Chat

Hi guys, Ive been programming in C for a while now, but my C tends to
be "baby C",  in that I probably don't write things as simple as they
can be written. . . Could someone please explain the entire purpose of
the following line, particularly the 1<<UDRE and why a bitwise AND is
being performed with UCSRA. I understand what the code does in the
microcontroller, just not what the statement in the brackets is saying. 

while ((UCSRA & (1<<UDRE))==0);

Please dont be afraid to insult me by explaining it simple, im very
keen to improve my coding level as my jobs become more complex.

Thanks
Hein B
Auckland, NZ