what does it mean when your period is extremely light and only last three days?

Usually nothing. If you're concerned, because the "nature" of your
period has recently changed, contact your gynecologist.

every girl/woman has her own duration of periods. its usually constant
with a devation of one day on either side. so if the period is
extremely light and lasts three days, its perfectly normal given that
fact that its same for most of the cycles.

hope that will help :)

how old are you?  periods can be very tempermental. I'm in my 40s so I
know about what I went through. Went from 7 day periods to 10, then to
5, then to 3, then back to 5.....  It can mean nothing.  When you
don't get your period, then you need to worry.  If your period lasts
longer than normal for 2 cycles, then you could have a fibroid which
is a benign tumor.  Anything abnormal to your doctor willl necessitate
an ultrasound with transvaginal imaging.  No big deal, I have to have
this done every 3 months because I have a few fibroids.