Just the current search, but the problem is millions of pages run third-party ads, and most are run by very few networks. These ad networks can aggregate the terms and then they have previous searches as well.
There's been various HN posts about how people circumvent browser privacy settings to track you across websites and even tricks such as generating an almost unique key by hashing together browser, fonts installed, IP address, etc.. I'm not sure of the current state of play in that war though.
I guess if you really don't want people to track private searches with your accounts, use a whole other browser where you're not logged into Google in incognito mode.
Edit: judging by the downvotes, I guess a good bunch of hackers like to live in atrocity!
Many people omit the word, "temporary". The suspicious part of me says they do it so their (mis-quoted) statement appears more bold and uncompromising.