Now that software has been around for a couple of decades, the companies that produce software have to deal with their (sometimes embarassing) earlier efforts. They have two kidnapped two words to describe old software; depending on which they use helps you understand the status of the software:
Classic - this word refers to old software that the company still approves of.
Legacy - old software the company wishes would go away, but can't get rid of because that would tick off too many customers, never mind raise the interest of government investigators.
This is, after all, an industry that considers itself young, so they couldn't possibly use "old" to describe old software. Kind of like the baby boomers who run it.