Answer: metals.
Justification:
There are 118 elements which you can find in the periodic table ordered by atomic number. Those elements my be classified into metals, non-metals and metalloids.
The metals are placed on the left side of the periodic table. The metals share the properties of luster, conductivity and flexibility.
The properties of non-metals (which are on the right side of the periodic table) are opposite to those of metals: opaque, low conductivity and brittle.
Metalloids have in between properties.
Copper, for example is a metal: it has luster, is flexible and is highly conductive of the electricity (and temperature).
