What are OVAs and how are they different from Specials? I often see that a lot of Anime series have a few extra episodes. Some are explicitly labeled as Specials, others labeled as OVAs. I get Specials, but I don't quite understand the term OVAs.

I googled, and found this: What is the difference between an OVA and an OAV?, but all I understood from it is that:


  OVA/OAV stands for Original Video Animation


Now that doesn't explain much, does it? So my question is, how is it different from other extra episodes (Specials)? Are they the same thing and the producers use the terms interchangeably or something else?
Broadly, the two terms could be interchanged, although there are a few points of (almost) difference:


OVAs are generally released for home video (be that VHS, DVD, or whatever), whereas it's possible for a Special to be released as a television broadcast that is just separate from the rest of the show.
OVAs are often shorter than a normal episode of the show, while Specials are often as long or longer, although this definitely doesn't always hold.
Some OVAs are not associated with a show, so they aren't a "special episode" of anything. For example, the series Video Girl Ai was only ever released as a 6 episode straight-to-video OVA.