Keyword searches are searches that use whatever words you plunk into the search box. Keywords are typically the most important words in your topic.
Most databases and search engines will tear apart words that are input side by side: For example, national ice cream day. Searched as a keyword search--national ice cream day--in JSTOR pulls up 111,127 results. There are a large number of results because national ice cream day, the four words, are being torn apart. They're appearing in your results glued together, but they're also appearing separately. So conceivably, you could have a result by John National whose article contains the words ice, cream and day.
To glue these two words together, you'll need to phrase search. Phrase searches "glue" keywords that normally appear side by side together. To phrase search, put your phrase in between quotes, like so: "national ice cream day".
Searching "national ice cream day" as a phrase, with " " around the words to glue them together in JSTOR pulls in 1 result. This is a significantly smaller number, and a number that will contain far more relevant results.
Phrase searching works with most databases and search engines (Google, Google Scholar), but if it does not--check the help area for more information.