Metal does not actually have a solid definition since it is a broad term. However, they are usually described as substances with high electrical and thermal conductivity as well as malleability and lustre. Metals usually loses its electron to form positive ions known as cations.
Metals can be defined by their properties: they are malleable, so can be shaped by hammering and bending; tough and fairly elastic, so can sustain considerable stress without breaking; and dense and highly reflective, so capable of taking a good polish. They are also good conductors of heat and electricity.