[michaelt]

The law is complicated, but basically if you're not an insider, information becomes public when you, a member of the public, notice it.

If you're at the airport near google HQ and you the CEO of a struggling AI startup arrive and hail a taxi to the google offices, and you think an acquisition might be on the cards? You're free to trade on that information, anyone in the airport could have recognised that guy.

Some complexity arises because insiders aren't allowed to tip you off. If you're golf buddies with the CEO of a struggling AI startup, and he tells you he made a business trip yesterday and Moffett Field is a great airport? If you figure an acquisition is on the cards and trade on that, it's insider trading.