Detergent

A detergent is a compound, or a mixture of compounds, that have a region that is hydrophilic, and dissolves easily in water, and another region that is hydrophobic, with little (if any) affinity for water. As a consequence, these compounds can aid in the solubilization of hydrophobic compounds in water, and usually are optimized for this property.

Though soap also has these properties, soaps in general are not considered a detergent. This may be more a function of history, as soaps have been known for hundreds of years, and detergents (often called synthetic detergents, to distinguish them as organically synthesized compounds) are products of the modern chemical industry.