The word for universe in Sanskrit is "Brahmanda", which is made by joining of words "Brahma" and "Anda". Brahma is derived from root "Briha" meaning to expand and "Anda" means egg. Thus "Brahmanda" means expanding egg. The universe is described as an egg in most post-vedic scriptures.
"Apah were indeed Salila earlier. Desire arose in it. They labored. From that heat arose. From heat golden egg was born. Golden egg was swimming in that for a year." Shatapatha Brahmana 22.214.171.124
"Whole universe including moon, sun, galaxies and planets was inside the egg. Egg was surrounded by ten qualities from outside." Vayu Purana 4.72-73
"At the end of thousand years Egg was divided in two by Vayu." Vayu Purana 24.73
"From that golden egg earth and heaven were made." Manusmriti 1.13
In Matsya Purana 2.25-30 following story is told about creation. After Mahapralaya, dissolution of the universe, there was darkness everywhere. Everything was like in a state of sleep. There was nothing, either moving or unmoving. Then Svayambhu, self-being, manifested, which is the form beyond senses. He created water first and established the seed of creation into it.