What data is it that Google collects without telling the user? Granted, they don't issue some pop-up notification or e-mail for every piece of data they collect

What data is it that Google collects without telling the user? Granted, they don't issue some pop-up notification or e-mail for every piece of data they collect, as the collect it, but every user has full access to all of the data points Google collects. They are highly transparent about the data they collect and even give users the option to delete that data from Google's records. I could be mistaken, however, so I'm curious - what data does Google collect without telling the user, at least by making that data collection transparent?