A varietal in the strictest term refers to the type of tree but is often used to refer to a growing region or a given plantation.
Roast type or roast name generally refers to are how dark a given coffee has been roasted. See roast names.
A blend is a blend of coffees from different regions. The idea here is to create something that is better than the individual coffees by themselves or in many cases this is used as a cost saving measure.