Originating in India before written history; Ayurveda is one of, if not, the oldest form(s) of life medicines, still in practice today, in the world. Ayurveda is often translated as the "science-of-life" but may be more accurately defined as life - "ayur," knowledge or knowing - "veda." Unlike western medicine or Allopathy, Ayurveda focuses on treating the health and well-being of the individual rather than symptoms of a disease. Although Ayurveda is designed to be largely preventative by practicing its principles everyday, it can be very useful to bring the body back into balance and thus providing relief for many ailments. Ayurveda's balance is based on the foundations of the three doshas: vata (air and ether/space), pitta (fire and water) and kapha (water and earth). Ayurveda believes based on many factors including but not limited to; your parents or genetics, environment, food intake and daily habits, leads you to a balance or imbalance, vikrti, with your true nature/constitution, prakrti.
An individual's prakrti is determined at birth and can be dominated by one, two or rarely all-three doshas. For example, if prakrti equals 100%, a single-doshic vata constitution could be something like 60% vata, 25% pitta, 15% kapha; a dual-doshic pitta-kapha constitution might be 20% vata, 40% pitta, 40% kapha; and tri-doshic constitution would have similar or equal levels of each dosha such as 35% vata, 35% pitta and 30% kapha, or 33.3% vata, 33.3% pitta and 33.3% kapha which is once again very rare. If you would like to determine your prakrti you can take a test on AyurvedaDosha's website here. Although the best way to determine your true prakrti is in person using your pulse, this test can give you an idea of where you stand. The main goal of Ayurveda is to bring and then keep you in balance with your prakrti.
So... Vikrti. Vikrti, is what levels of doshas are present in an individual as a result of the factors listed above. Your leading dosha(s) are the ones most likely to go out of balance first.