What does varietal mean in coffee?

In coffee, varietal refers to the botanical variety or cultivar of the coffee tree - the specific genetic population from which a given coffee was produced. Geisha, Caturra, SL28, Bourbon, and Typica are all varietals.

Strictly speaking, the technically correct term is cultivar (a human-selected variety), while varietal refers more precisely to a naturally occurring botanical subdivision. The term is borrowed from wine, where a varietal wine is made from a single grape variety. Coffee adopted the usage, and while cultivar is more botanically accurate, varietal is what the industry uses.

Understanding varietal matters because different varieties express different flavour characteristics - particularly at altitude in optimal conditions. But varietal alone doesn't determine cup quality. Growing conditions, processing, and farm management all interact with genetics to produce what ends up in the cup. A Typica at 800 masl, poorly processed, will be eclipsed by a Catimor at 1,800 masl, carefully managed. The variety sets a potential; everything else determines whether it's realised.