Subject: O/D
Question:

I was driving my car at night and then a small light on the dash board lit up telling me that the O/D is off, what is an O/D?(a mitsubishi galant '94, also have a problem with the fan belt it keeps on slipping and making a squeaking noise) 

Answer: Edel,
The O/D light indicates your OverDrive setting. It's a function of your transmission to allow your car to travel at highway speeds, but maintaining lower RPMs. It's usually controlled by a button located on your gear shifter. Look for that button and push it. See if that turns your O/D light off. If pushing that overdrive switch does not turn off the light, you should take your car in to get it looked at. This would also be a good time to get that squeaky belt replaced as well.
Good luck!