Economists / anti-trust lawyers (at least in the US) look at a butt-ton of variables, and there is significant literature on the topic (source: I have a graduate degree in Economics - and love to talk about this type of stuff,) but just some of the top variables included:

1) Market definition (to your point - in the tech world, this can get problematic very fast.) 2) Market share 3) Market share rank (i.e. 4% among a million competitors who all have <1% would be pretty significant) 4) Ease of entry into a market (i.e. Google gets a lot of scrutiny in the search market because of the consensus that to build a good search engine competitor, you need a lot of data for machine learning models, which a startup can't just get $ to buy and/or cleverly build with IP.) 5) Ease of customer switching 6) Pricing behavior ...among many others.

Historically, a lot of analysis & literature to demonstrate market dominance has been on elasticity of demand: e.g. if I as dominant company X adjust prices, and customer demand doesn't change (probably because there are no substitutes and/or the switching cost is too high,) then anti-trust regulators would probably be all on my ass. But in the tech world, new models are still being developed I think, as that concept is not 100% applicable.

That reporter is right though: Walmart isn’t a monopoly. Not generally.

It can have a local monopoly of course (and often does in many more rural areas) but that’s not the same.

I think I’ve been to a Walmart once in the last 10 years. I’m not even trying to avoid them: there’s no reason or need for me to go there and I have plenty of other (just as cheap) options.

That’s not a monopoly.

They’re a massive business and a dominant national brand but that’s also not a monopoly.

In case it wasn't clear, my point was that the percentage is not the indicator of monopoly or non-monopoly. I'm not arguing that you should agree Walmart is a monopoly.

That said, your experience and you having other purchasing options isn't the only criteria, as @s3r3nity pointed out. Being on Hacker News probably means you're not in the lower 50% of the US population socioeconomically.

Being a massive business is precisely one way Walmart might be considered a monopoly. They're not a dominant national brand, they are the single largest global brand on the planet by revenue. The fact that if Walmart closed tomorrow, it would have a significant negative impact on the US economy is alone enough to warrant asking the question. When a company is "too big to fail" that automatically puts it in the potential monopoly category.

Also, there have been anti-trust cases against Walmart, some of which Walmart has settled. So it's really not super clear cut that Walmart isn't a monopoly.