Fundamentally, the difference between aperitifs and digestifs seems clear: aperitifs come prior to a meal, and digestifs afterwards. However, there is lots of complexity.
Popular in European countries like France and Italy, an aperitif is a pre-dinner drink that's also a ritual. Typically, its palate leans dry, a little fruity, and low in alcohol.
It can be a commonplace drink like a dry white wine or a highly aromatic fortified wine or liqueur. Aperitifs may be served straight, but are often crafted into unfussy cocktails.
Enjoyed post-dinner, the digestif is a stark contrast to the aperitif. It's a slow-sipper also full of flavor, but meant for relaxed sipping, unlike an aperitif's zippy nature.
Common selections include sherry, vermouth, regional versions of brandy, whiskey, cognac, and aged tequilas. Nearly any barrel-aged spirit can be a digestif.
Many digestifs have similar production methods to aperitifs, but resulting in a more intense palate. They are a final lasting impression meant to aid digestion.