Google's only product is online advertising, the only kind of advertising that matters in the 21st century.

This is a big deal because they can abuse their advertising clout for evil purposes. (E.g., advertise Chrome but put out a prohibitive pricing scheme for Firefox.)

But it's not a monopoly yet because Facebook and Amazon are competing actors in this space in the USA, and other nations have their own local actors.

In theory, though, if Google went on a really aggressive attack via their Chrome, Android and Analytics properties then they could kill off the competition.