I think the Doc has covered this but I just wanted to add that the reason that I don't believe it is elitist is the same as the reason I don't believe that BSO means cheap bike.
A new cheap bike can be had from the likes of Decathalon or
Halfords, or second hand from
ebay, Gumtree, local free ads or even from a chap you only know through a cycling forum. They can be fanstastic things, offering reliable transport at bargain prices.
A BSO will start off as a POS which is so heavy that it's difficult to ride. If it lasts past the first 100 miles, things will have fallen off or worn out or be unserviceable but the chances are that the bike will be such a burden to the potential cyclist that it will be left to gather dust and house spiders long before it makes that milestone.
BSO does not mean cheap. My kids both have Apollo bikes from Halfords which cost around £120 two years ago. Both have proved resilient and reliable and, my daughter's particularly, they have covered some fairly decent miles without needing anything more than the saddle raising because the kids are growing.
Conversely, my son's bike before that was a Reebok which never really did have a decent rear brake and seemed to weigh about the same as my car.
That was a BSO.