A herb refers to a herbaceous plant – A plant which has no distinguishable woody stem above ground but leaves and stems at the ground level, and which die after the growing season comes to an end. Herbs may be perennial, biennial, or annual.
Perennial and biennial herbs are those herbaceous plants which have some parts that survive even after the rest of the plant has died at the end of the growing season, and the new plant grows from these living parts. Annual herbaceous plants die completely at the end of the growing season, or after they have produced flowers and fruits, and the new plant germinates from a new seed.
A herb is primarily used for culinary, spiritual or for medicinal purposes. It is usually valued for any of its parts- roots, stem, leaves, flowers, seeds, fruits or any other part.
Herbs used for culinary purposes are generally valued for their scent or flavour and are used in preparations of dishes. A herb is different from a spice- herbs generally refer to the leafy green parts of the plant used in cooking, while spices are commonly derived from other parts of the plant. Herbs are also different from vegetables in the sense that they do not form a main part of the food, but are added mainly for colour or scent or flavour.
Medicinal herbs are used in traditional medicine for their phytochemicals, which supposedly have a beneficial effect on the body. However, large doses of herb extracts can be toxic for the human body. Some herbs, such as cannabis, are used for recreational purposes.
Other herbs like frankincense and myrrh (important in Christianity) and basil (called tulsi, important in Hinduism) are used for spiritual purposes.