Keyword-A keyword is essentially any word or phrase you use when searching with a search engine.” In a simple language, any single word related to your business, product/services which can be useful for your business.
eg. If you are selling shoes online then “shoes”, brand name like “Reebok”, “Nike” are your main keywords.
Keyword Phrase- Combination of those keywords is called key phrase.
eg. As per the same example for online shoe store above phrases can be (“Sport shoes”, “Reebok shoes”, “school shoes” etc.)