Sealcoat is a liquid that is applied to asphalt

Asphalt concrete

Asphalt concrete is a composite material commonly used in construction projects such as road surfaces, airports and parking lots. It consists of asphalt and mineral aggregate mixed together, then laid down in layers and compacted...

 to protect it from oxidation and the damage caused by winter cracking, as well as the UV Rays and traffic. In areas of the world that experience freezing and thawing, the reapplication timeline will likely be sped up.

Benefits

Sealcoating is not only a cold climate need. Since asphalt is a petroleum product, other petroleum products will react with the surface. This includes vehicle oil and gasoline. The sealcoat will act as a barrier against those materials. It should be noted that a sealcoat is not a crack filling agent, this must be done prior to applying the sealcoat.

Controversy

Use of such sealcoats is illegal in certain jurisdictions as certain brands can contain concentrations of coal tar of up to or greater than 30%.