A saucepan is a cooking vessel generally used on top of a range for heating food and / or reducing sauces.
Saucepans can be made of a variety of materials, like aluminium and stainless steel, and the cooking surface can have a non-stick coating, like Teflon. As with all pans the heavier the gauge of the metal the better (especially at the base); it enables more even heat distribution, which makes sticking and burning less likely. Some saucepans have a thick sheet of thermally conductive aluminium laminated into their base for that purpose (like the one shown). A coating of copper on the base allegedly has the same effect, but it would need to be reasonably thick to have any real benefit.
High-sided sauce pans are most useful for heating foods with high liquid content. Low-sided and flare-sided (called Windsor pans) saucepans are most effective for reducing sauces and other liquids.