Yoga is an ancient art of living dating back around 200 years BCE. It is the practice of a set of breathing exercises and postures aimed at providing physical and mental well-being.
There are several forms of yoga, each focused on a specific aspect of the practice.
For example, Vinyasa is a rather dynamic yoga during which the sequence of postures is done to the rhythm of breathing, with the aim of strengthening your body while improving your flexibility, but also your cardiovascular system.
Iyengar is a more static yoga, focused on body alignment. Finally, Hatha yoga is a much gentler yoga, more accessible to older people for example.