bash, expressions, ???

["Egor Tur" <worldeb@ukr.net>]

Hi.
Who can explain?
ps ax | grep lpd
  398 ?        S      0:00 lpd Waiting  
 5593 pts/13   S      0:00 grep lpd
ps ax | grep [l]pd
  398 ?        S      0:00 lpd Waiting

What do [l]?
Thanx.