According to the Yoga Sutras by Patanjali, a collection of 196 aphorisms on yoga dated between 500-300 CE, yoga is defined as:
योगश्चित्तवृत्तिनिरोधः ॥२॥
yogash-chitta-vritti-nirodhah ||2||
Yoga is the silencing of the modifications of the mind
Therefore, yoga can have many different manifestations and it is not necessarily bound to the practice of physical exercise.
There are indeed many types of yoga and it is a personal preference to choose one rather than another. The most well-known types of yoga in the West are Bhakti yoga, Raja yoga, …………
What differentiates them is usually the techniques used
However, Patanjali clearly states that yoga can be conceived as a ladder with 8 steps (Ashtanga yoga): Yama, Nyama, Asana, Pranayama, Pratyahara, Dharana, Dhyana, Samadhi.
Yama : this is the set of ethical rules that we need to observe in order to live a respectful life, towards ourselves and the external world. It is composed by 5 specific rules: Ahimsa (non-violence), Satya , Asteya (non-stealing), Brahmacharia (con……) , Aparigraha
Nyama: this group of rules indicates how we can take care of our inner selves, and especially of our spiritual side. There are again 5 advices: Saucha, Samtosa, Tapas, Svadhyaya, Isvara pranidhana.
Asana: at this point in time, everybody knows this aspect of yoga. Asanas are body postures which help to take care of our physical body, creating health benefits for internal organs and systems as well as keeping the body in the best possible shape.
Pranayama: this includes a vast number of breathing techniques, each one with different effects (in particular on the nervous system).
Pratyahara: this is the start of the hard work. It is the exercise of withdrawing from the external ‘whirlpool’ of events, and start observing ourselves and our behaviour in order to become more and more detached by any practical objects and disturbing feelings.
Dharana: once we have learnt not to be so involved in the world anymore (not necessarily abandoning our everyday activities!), we can start exercising about guiding our mind towards concentrating on one fixed point of attention (being a part of our body or a thought/idea).
Dhyana: this is pure meditation. There is no need to do any action or focus on one point, because the mind in this state is simply present to itself and does not feel the need to move in and out of thoughts, or to drive the body.
Samadhi : when you manage to calm all the external and internal distractions that can affect the mind, you can truly experience the deep connection with every element around us and recognise how much peace pervades everything. This eternal state of blissful, universal connection without effort is the ultimate goal of yoga.