A Foley Artist is somebody who creates the “normal” sound effects for a movie, such as footsteps, doors opening, etc.
Barry
Foley artists create all the incidental sound effects that you hear in the movie. Crunching leaves, fists hitting faces, champagne corks popping and the like.
The foley artists are the people who do the sound effects like footsteps, spines being crushed (celery is good for this) and horse hooves (cocoanut halves, in the old days). Basically any sounds that aren’t recorded at the time of filming. ‘Looping’ is the recording of the actor’s voices, frequently done after filming.
Explosions, gunshots and screeching tires, things like that, are usually taken from sound effects libraries. But the foley artists are watching the film and trying to match the noises they are creating (walking, clicking, clacking or crunching, ect.) with the on-screen actions.
Although you’ve gotten good answers already, you might look at http://us.imdb.com/Glossary/F for their explanations.
Today’s UserFriendly Link of the Day happens to be Art of Foley. I haven’t read it, but it looks informative.
Well, I learned something new today. I was afraid it was the person in charge of catheters.
Chefguy, I can’t pass up the opportunity to be straight man for you. Just what connection did you see between foley and catheters?
A Foley Catheter is a tube that drains urine from the bladder. Hey, you know how weird those Hollywood types are…
Me, too! 
I was Foley confused, but now I Foley understand.
AwFoley nice of you guys to clarify that.