For example, console hardware is loss leader for console makers because they make up for it for every game sold. Google Chrome and Android are loss leaders for Google, but are strategic assets protecting its revenue business.
In both cases, these companies can continue to do that indefinitely (as long as it makes business sense).
Venture-backed companies that are burning cash, on the other hand, are pursuing an unsustainable strategy of predatory pricing to kill off competitors and grab the most of the market.
(obviously, it's not either-or, you can easily name examples from long standing companies or startups doing either)