An alloy is a homogeneous mixture of two metals; a solid solution. The two metals have not combined chemically into a separate compound. The alloy has physical properties intermediate between those of the constituent metals; but the chemical properties of each metal remain unaffected. An alloy can be separated by physical means (separated by melting).
A compound is the product of a chemical reaction between different elements or compounds, and is featured by chemical bonding, with the sharing or transfer of electrons. A compound cannot be separated into its constituent elements by physical means.