I set the bar even lower than the other commenter. I don't care if it's a monopoly, nor even really if it's engaged in anticompetitive practices. I just care if it's big, like big enough to have outsized market power. I think that markets with large disparities in size and market power among participants are inherently anticompetitive. I think that in most market sectors --- banks, automakers, airlines, media, you name it --- there are a small number of large companies with outsize market power, and those should all be broken up.

The lawsuit focuses specifically on search and search advertising. So the answer to your question is Google Search.

Note that a legal monopoly is not the same as the extreme simplification of "zero other options". "In law, a monopoly is a business entity that has significant market power, that is, the power to charge overly high prices, which is associated with unfair price raises." [1]

"In United States v. Google LLC, the federal government alleges that Google has unfairly hindered competition in the search market through anti-competitive deals with Apple as well as mobile carriers. The government alleges that, as a result of these practices, Google has accumulated control of around 88% of the domestic search engine market.

In doing so, the government alleges, Google has additionally monopolized the search advertising market at the expense of competing services. Per the government's estimation, Google has been able to accumulate control of over 70% of the search advertising market. As a result of lack of competition, Google has been able to over-charge advertisers versus what they would pay in a competitive environment." [2]

Statcounter seems to align quite closely with the government's assertion. [3] Extra creepily, it appears to be even a hair worse globally, where Bing is less used (not that I like Bing or MS either). [4] But there is no international framework I'm aware of to handle global-scale monopolies, so that's outside the scope of the suit.

[1] https://en.wikipedia.org/wiki/Monopoly [2] https://en.wikipedia.org/wiki/United_States_v._Google_LLC_(2... [3] https://gs.statcounter.com/search-engine-market-share/all/un... [4] https://gs.statcounter.com/search-engine-market-share

I didn't use that word and no one in the chain above me did either. I specifically chose "anticompetitive behavior" to emphasize that a monopoly is not required to do damage to the free market or to trigger antitrust action.