The courts don't use "monopoly", they use the term "monopoly power": https://www.ftc.gov/advice-guidance/competition-guidance/gui... Like this says, it doesn't strictly require a monopoly.

It's just a term that gets simplified by journalist and articles, because no one is familiar with monopoly power.

From the court filing:

> Plaintiffs have proven that Google has willfully engaged in a series of anticompetitive acts to acquire and maintain monopoly power in the publisher ad server and ad exchange markets for open-web display advertising.