Business Objects in Unix environment

Can anyone explain to me what I am seeing when I submit this unix command on my Business Objects report server:

ps -ef | grep nikutst

I get several lines that show:

nikutst 23886 15890 0 Feb 25 ? 0:37 Xvfb :2 -screen 1 1024x768x24 -sp /opt/CA/SharedComponents/CommonReporting/bobj

There are about six of these lines at any given time. The only difference between each line is "Xvfb :1". Each line increments, such as "Xvfb :2", "Xvfb :3", "Xvfb :4", etc...

Anyone know what these are?