Ayurveda sees everything — including us — as combinations of five great elements: Akasha (ether/space), Vayu (air), Tejas (fire), Jala (water) and Prithvi (earth).
These elements pair up to form the doshas: air and ether make Vata; fire and water make Pitta; earth and water make Kapha. The qualities of the elements (light, mobile, hot, liquid, heavy…) are exactly the qualities you feel in each dosha.
It is a poetic, observational language — a way of describing the textures of nature and of your own experience, rather than chemistry in the modern sense.