Asphalt is a petroleum derivative. Is refined as a heavier hydrocarbon from the process of making many other petroleum products. It is generally lumped in with other aliphatic hydrocarbons which are not evaporative.
Tar, or more correctly coal tar, is a derivative of coal. It is significantly diffent in properties than asphalt. Like asphalt, it has many uses from being an additive to paint, wood preservative (creosote), to roadway materials, to roofing materials. It is more waterproof than asphalt, but has been labeled as a carcinogen and its use has been curtailed over the past 20 years.
Bitumen is a generic class of materials that can refer to either asphalt or coal tar. The most common references are for modified bitumen roofing materials (usually asphalt based, but there were a few coal tar modified bitumens on the market for years). The "modified" means that the parent material is mixed with something else, usually a closely linked hydrocarbon, to give it better properties. For instance, styrene-butadiene-styrene (SBS) is mixed with asphalt to give it more rubbery properties.
Either asphalt or coal tar can be emulsified; however, coal tars cannot be diluted as easily with solvents as asphalts. Most aromatic solvents (xylene, toluene, etc.) have little or no effect on coal tar, but will readily dissolve asphalt.
"Tar" is a term that is erroneously applied to almost any black, gooey substance used in construction. It should actually only be used to refer to coal tar derivatives.
