Our Knowledge Base is powered with a global search feature, which allows to type in a few keywords and find all articles that contains them. It also automatically suggests relevant articles based on the typed in keywords on a go.
But if your customers are searching for some info and find nothing, you'd probably want to know about it as this information can be a great source of ideas for new articles.
That's exactly what the 'Failed searches' report is for. Every time someone types in a keyword and finds zero results, you will know about it. Choose a period for which you want to see all the failed searches.
Also note that this report is updated in real time.