Honey is a product produced by bees (as stored food) from the nectar of flowers. Next to water, it is the main ingredient in mead. It is also an excellent sugar substitute for medieval recipes, containing mainly a combination of glucose and fructose - along with the complex honey flavours. Note: many supermarket honeys are actualy "cut" with extra glucose - which makes it runnier (useful for spreading), but less flavoursome.
It also has many medicinal properties which modern doctors are now rediscovering. A classic throat soothing drink is lemon and honey, but it is also used for healing wounds and for treating eczema.