An alloy is a mixture made by mixing two types of elements together in which at least one is a metal.
Solder is a type of alloy of lead and tin that is used in electrical circuits.
The alloys of tin and lead have characteristic weight percentages in which 63% tin(Sn) and 37% lead (Pb) combines to form solder. When the concentration of tin is more than lead, such types of alloys are also called soft solders.