You would have seen people performing these kind of postures-
In simple terms, this is Asana; more precisely Yogasana, since asana is part of Yoga (both asana and yogasana mean the same)
Pathanjali's sutra for asana is-
स्थिर - steady
सुखम् - comfortable
आसनम् - asana
Which means a posture which is steady as well as comfortable is an ...
Is there any scriptural ( Vedic or Puranic ) reference for all matter coming from Akasha and Prana?
Yes, the Taittiriya Upanishad says all elements come from ether:
tasmAdvA etasmAdAtmana AkAshassambhUtah | AkAshAdvAyUh | VAyuragnih | AgnerApah | adbhyah prithvi | prithivyA oshadhayah | oshadhIbhyo'nnam | annAt purushah
From that Brahman sprang ...