ONA is very different from OVA or OAV or (Original Video Animation, Original Animated Video) OVA/OAV is created for solely selling purposes or market a video while unlike in ONA which defines as Original Net Animation this Videos are directly release or uploaded onto the World Wide Web or the Internet. To begin with, almost all ONAs(Original Net Animation) are independent  releases or fan works maybe the creator don't have enough budget funds or support so decided to upload it Online or just fairly a love for Anime. Did you know that that the term ONA first emerge when creators of the Anime "Lingerie Fighter Papillon Rose" because there was no other word to describe this kind of Anime format. Then Anime News Network decided to adapt it for used to there Encyclopedia since they felt "ONA" was an original and appropriate denomination.