According to The Complete Metalsmith (a classic and indispensable reference if you work with non-ferrous metals), "white metals" refers to a group of soft grey metals with low melting points (such as lead, tin, cadmium, bismuth, or any alloy with one of the aforementioned as its primary ingredient). These metals are also sometimes refered to as type metal, since they have often been used in the making of printers' type.
Fumes produced when melting these metals are hazardous, and caution should be exercised when handling them. Lead, in particular, can be absorbed through the skin. If you're working with any of these metals, do it in a well-ventilated area, avoid eating or drinking or smoking in the vicinity, and wash your hands well afterwards.