See also: Keywords
From the perspective of the user, a keyword is what someone types into a search engine when they want to find something specific.
It can be a single word or a combination of words, e.g. ‘rose’ or ‘rose species red’. If the latter, it is sometimes called a keyphrase.
From the perspective of the SEO specialist, keywords/keyphrases are terms added to online content in order to improve search engine rankings for those terms. Most keywords are discovered during the keyword research process and are chosen based on a combination of search volume, competition and commercial intent.