What is Molded Parts Trimmers and trim the flashing off the molds mean?

At one time every little kid of age five or so knew very well what sprues and flashes were. Here are pictures: www.google.com/search?site=&tbm=isch&source=hp&biw=1024&bih=739&q=sprue+in+casting

When they make the mold for plastic or metal models, they arrange all the parts on a flat surface, connected by a rather large shaft of plastic called a sprue. That is where they force the plastic into the mold, and the sprue carries the molten plastic to all the individual pieces. If the two halves of the mold don't match perfectly, some plastic is forced into the place where they don't meet, and those bits of plastic are called flash. You might also have a large place away from where they poured the plastic in. That is a riser, just to be sure the air has a place to get out of the mold.