In early English usage the word "herb" was synonymous with vegetables. It later became restricted to parts of vegetables that grow above ground. For example a turnip was a vegetable and the leafy top was called an herb.

The botanical definition of an herb is " a plant with a fleshy not a woody stem, which, after the plant has bloomed and set seed, dies down to the ground." This is not a perfect definition because herbs like sage, thyme, and rosemary have more or less woody stems, although they are not covered with true bark.

An herb is a plant whose properties allow its use as a medicine. Most of the herbs we use today as seasonings were originally medicines. They served for centuries as the principle medicines of the times. They were kept in in pharmacies in dried form for availability all year. The English word "drug" is from the Anglo-Saxon drigan, to dry.

For Wiccans an herb is also a plant capable of producing magickal effects. Methods of gathering the herbs depended on the surround culture. For instance in Babylon magickal herbs were gathered by moonlight. They were considered to have to have the most power of the moon god Sin at that time.

For the cook, an herb is primarily a plant which adds flavor to food and drink, a seasoner. In medieval times it was customary to precede and follow a meal with an herbal drink.