An alloy is a partial or solid solution of one or more elements in a metallic atom lattice, can be single phase or multiphase depending on if its completely solved or not.
Examples of different alloys:
Steel: iron + carbon
High speed steel (HSS), contains: carbon, Chrome, Molybdenum, Tungsten, Vanadium,
Cobalt, Manganese and Silicon
Pig iron: approx 3.5-4.5 weight % carbon. Produced by 'smelting' iron ore with coke and using a flux (usually limestone)
Cast iron: iron, carbon (2.1-4%) and silicon
Brass: Alloy of copper and zink
Stainless steel: >12 weight % Chrome (Cr)