Smart Keyword Search is a Safari extension, that fixes one of the "missing features" in Safari. Many browsers allow one to customize the Omnibox (this is the address bar, which also functions as a search bar), so that certain searches go to certain websites.
For instance, one may want to make it so that if "imdb pulp fiction" is typed into the search bar, it actually searches for pulp fiction on the IMDB website, rather than search for "imdb pulp fiction" on Google (or whichever other search engine you have as deault).
This functionality is known as "Smart Keywords" in Firefox' Chrome has the same functionality (although without a clear name).
Safari used to have a plugin doing this (called Omnikey), however this plugin stopped working in Safari 13.
