Hatha Yoga is what,almost everybody,maybe 97% of the people in the Ocident and in this days also in Índia,start to pratice as yoga when he get in touch with a teacher,a school or a instructor of a academy.
Without knowing the most purists are also praticing tantra,.Hatha yoga is a tantric pratice "presented" by a Tantric sect ,the Nathas, as a stair that leads to Raja Yoga, Raja or Classic yoga as it was codified by Patanjali.
Hatha yoga was presented with six angas,the limbs of hatha yoga are defined as asana, pranayama, pratyahara, dharana, dhyana and samādhi.

As Raja yoga was codified by Patanjali with his famous 8 angas,Matsyendra natha presenting Hatha yoga as preparation to Raja,never intended that hatha was a yoga that alone can take the practicioner to the ultimate state of yoga,kaivalya,but Matsyendra Natha knowing the difficulties that the body of practitioners were subject,recovered the yoga of Patanjali,who was half-forgotten by these times,introducing the preparation of the physical body of the yogue, vajra deha.