I've always understood bootstrapping in the context of startups to mean that the business achieves sustainability through customers, not loans, equity deals, etc.
Ash Maurya has a blog post from a few years ago that appears to define bootstrapping as the above, plus that the product is developed without any customer feedback before the product is ready to sell.
To me, this sounds like the "Lean Startup" myth, that being before the lean startup approach that startups did not talk to customer before they had a product to sell.
Is Ash Maurya's use of the term bootstrapping a commonly understood use of the term?
SOURCE: "Bootstrapping a Lean Startup "
I believe bootstrapping to be purely about funding (or lack of external funding to be precise).
When and how you get customer feedback is unrelated to the "bootstrapping" term.
Bootstrapping = growing your business from profit (instead from outside development). I have been (successfully) bootstrapping a web app software (service) business, and now I'm bootstrapping product businesses. Bootstrapping a service business is quite easy: just find a first customer, and there you go.
Bootstrapping a product business is much more difficult though. It requires a big upfront investment, as a product pays it back over time. However, a product is scalable, while service business is not.
What I love so much about Bootstrapping is that you don't owe anything to anyone, it's 100% your own business, and the fact that you can turn 0 dollars into several thousands of dollars with only your time as input, is amazing.
As Joel said, in my understanding Bootstrapping is purely about financing. Basically using your own capital to fund the company until you generate enough revenue to attract investors, contrary to a typical startup attracting investors pre-revenue stage.