Keywords are the search queries that we use to search anything on search engines like Google, Bing & Yahoo. Best queries or keywords are those that best describes the searcher purpose to search anything that they were looking for. Keywords are divided in two categories:
These short tail and long tail keywords or queries are used to make the web available against those keywords or search queries that were chosed targeting the niche. There are tools and methods that are used to find those search queries through your website could be searched on the search engines.
As far as keywords research tools are concerned. Google Adwords, Trends, Insight, word tracker and many more are used to find the relevant and conversation generated keywords to make web more and better searchable.
Video here: Filtering Keywords Using Semantixpro