Yog in Hindi language, we mean addition(+), example yog of 5+4=9. Here Yog is refered as meeting/addition of Atma(Human) and Param Atma or Parmatma(God). So Yog is Atma+Param Atma. Casually we assume Yoga is only Asna(Pose). But Asna(Pose) is a small part of Yog.

As per Ashtatang Yog (Asht means 8 And Ang means parts (Limbs),

Ashtanga yog literally means "eight-limbed yoga," as outlined by the sage Patanjali in the Yoga Sutras. According to Patanjali, the path of internal purification for revealing the Universal Self consists of the following eight spiritual practices:

Yama [moral codes]
Niyama [self-purification and study]
Asana [posture]
Pranayama [breath control]
Pratyahara [sense control]
Dharana [concentration]
Dhyana [meditation]
Samadhi [absorption into the Universal]

The first four limbs—yama, niyama, asana, pranayama—are considered external cleansing practices.

Whereas next four limbs: pratyahara, dharana, dhyana Smadhi-- are considered internal cleansing practices.

For each limb,there are sub-limbs.

The four internal cleansing practices—pratyahara, dharana, dhyana, and samadhi—bring the mind under control. When purification is complete and mind control occurs, the Six Poisons surrounding the spiritual heart [kama (desire), krodha (anger), moha (delusion), lobha (greed), matsarya (sloth), and mada (envy)]—"will, one by one, go completely", revealing the Universal Self. In this way, the correct, diligent practice of Ashtanga Yoga under the direction of a Guru "with a subdued mind unshackled from the external and internal sense organs" eventually leads one to the full realization of Patanjali's eight-limbed yoga.