Flavour
Ajwain tastes similar to thyme because it also contains thymol oil, but it is a bit astringent, and is stronger and less subtle than thyme. It is described as having a pungent and bitter flavour, and also as having a "musty and base" flavour.
History
Ajwain originated in the Middle East, possibly in Egypt. It is now primarily grown and used in India, but also in Iran, Egypt and Afghanistan. It is sometimes used as an ingredient in berebere, an Ethiopian spice mixture.
Preparation/Form
The dried fruits of the plant are used. Because they look like seeds, some call Ajwain, Ajwain seed. The flavour of this spice can be improved by roasting the small fruits in a dry pan.