Spotlight
Convert currencies and measurements. Enter a currency—like $, €, or ¥—and an amount, then press Return to get a list of converted values. Or specify a unit of measure for measurement conversions.
Use Siri Suggestions. Siri Suggestions offer info from Wikipedia articles, web search results, news, sports, weather, stocks, movies, and other sources when you search with Spotlight.
If you want Spotlight to search only for items on your iMac, open Search with Spotlight on Mac in the macOS User Guide.