Back in the way, before the dot-com burst and social media and HTML5, it was a fine art to search the internet. There was even a competition, with state finals and everything, related to searching the internet. At my high-school, the directive in these competitions was "Use a search engine, we suggest maybe use Google, that's looking like a good one. Here's how you use Boolean searching..."
You know boolean searching, right? "music AND madonna NOT kylie", should not return any results with the word "kylie". Try that in google now days. It returns kylie.
Google proper has ditched the boolean search for natural language parsing. A bit annoying, especially when it tries to guess synonyms and such (you can force your term to be used by wrapping it in double quotes, most of the time)
It's good that they didn't throw that code away, though, because boolean logic still lives in Gmail's filters. Searching for subject title words by separating them with the word OR will show you a union of the terms that will yield more results than the subset. Just remember that the order of execution is important, and I cannot, still, for all my trying, find a way to change the filter order other than deleting and re-adding it. Ugh.