pranayam!
by separation in two words of pranayam we get prana and aayam.

prana means vital energy of body and
aayam expansion and dimension

Basically oxygen or air is one of the source of vital energy of the body.
Breathing system provides us oxygen and that oxygen transfers to the body cells.

Pantanjali the guru of yoga told that, pranayama is basic of yoga and knowledge of it is must for a yogi,
it can cure any body problem.

there are various types of pranyama,
and the main pranayams are
1. Nadi Shodhan
2. Suryabhedan
3. Chandrabhedan
4. Sheetli
5. Sheetkali
6. Anulom Vilom
7. Bhastrika
8. Kapalbhati
9. Udgeeth
10. Bhrahmari