A small quantity of alcohol, food or other consumable, usually requested because the consumer of it: (a) does not want to get drunk, (b) does not know what it tastes like and wants to try it, or (c) knows what it tastes like, doesn't like it, but doesn't want to offend the person offering it. Also known as a "sensation".
Dinner-party host (holding wine bottle): Would you care for a glass of spinach wine? It's made from real spinach, that's why it's dark green.
Dinner-party guest (holding wine glass): Just a suspicion thanks.